Invasive plants differentially affect soil biota through litter and rhizosphere pathways: a meta-analysis

The Role of Mycorrhizal Fungi in the Inter and Intraspecific Competition of Nicotiana glauca and Vachellia gerrardii

A competition experiment between Vachellia gerrardii and invasive Nicotiana glauca Graham was conducted to assess the impact of Arbuscular Mycorrhizal Fungi (AMF) symbiosis on the inter and intraspecific competition between the two species. Seedlings were established under mono and mixed plantations with different species proportions (3:1, 2:2, 1:3) and plant densities (1, 2, 3, and 4 plants/pot) for mixed and mono planting respectively, with and without AMF. The vegetative growth parameters (height, leaf area and number, total dry weight/plant, relative yield, relative yield total), roots characteristics (length, surface area, volume, tips number), competitive interaction (aggressivity), and physiological traits (chlorophyll a, chlorophyll b, photosynthesis, stomatal conductance) were measured to evaluate plant responses to AMF symbiosis and competition. The results revealed that AMF symbiosis significantly enhanced the vegetative parameters (leaf area, height, and total dry weight) in both species under mono and mixed plantations compared to plants without AMF. Under AMF treatment, in the interspecific competition, most vegetative and root parameters of N. glauca were higher than V. gerrardii. At inoculant and species proportions, the relative yield of N. glauca exceeded that for V. gerrardii; however, N. glauca was more aggressive towards V. gerrardii. N. glauca root indices were higher than V. gerrardii under inter and intraspecific competition. Simultaneously, for both species, in monoculture plantations, most parameters decreased as plant density increased, wherein the decrease was higher for plants grown without AMF. Photosynthesis increased in AMF treatment, particularly for N. glauca. In conclusion, AMF promoted the growth of invasive N. glauca more than native V. gerrardii, particularly in terms of the root system. Our results provide a critical perspective that the AMF has the potential to contribute and facilitate the invasion of N. glauca, as well as support it with a competitive advantage over V. gerrardii, thus highlighting its potential role in shaping plant-plant interaction in invaded habitats.

Nitrogen Acquisition by Invasive Plants: Species Preferential N Uptake Matching with Soil N Dynamics Contribute to Its Fitness and Domination

Plant invasions play a significant role in global environmental change. Traditionally, it was believed that invasive plants absorb and utilize nitrogen (N) more efficiently than native plants by adjusting their preferred N forms in accordance with the dominant N forms present in the soil. More recently, invasive plants are now understood to optimize their N acquisition by directly mediating soil N transformations. This review highlights how exotic species optimize their nitrogen acquisition by influencing soil nitrogen dynamics based on their preferred nitrogen forms, and the various mechanisms, including biological nitrification inhibitor (BNI) release, pH alterations, and changes in nutrient stoichiometry (carbon to nitrogen ratio), that regulate the soil nitrogen dynamics of exotic plants. Generally, invasive plants accelerate soil gross nitrogen transformations to maintain a high supply of NH4+ and NO3- in nitrogen-rich ecosystems irrespective of their preference. However, they tend to minimize nitrogen losses to enhance nitrogen availability in nitrogen-poor ecosystems, where, in such situations, plants with different nitrogen preferences usually affect different nitrogen transformation processes. Therefore, a comprehensive understanding requires more situ data on the interactions between invasive plant species' preferential N form uptake and the characteristics of soil N transformations. Understanding the combination of these processes is essential to elucidate how exotic plants optimize nitrogen use efficiency (NUE) and minimize nitrogen losses through denitrification, leaching, or runoff, which are considered critical for the success of invasive plant species. This review also highlights some of the most recent discoveries in the responses of invasive plants to the different forms and amounts of N and how plants affect soil N transformations to optimize their N acquisition, emphasizing the significance of how plant-soil interactions potentially influence soil N dynamics.

The Role of Pathogens in Plant Invasion: Accumulation of Local Pathogens Hypothesis

In the past decades, dozens of invasion hypotheses have been proposed to elucidate the invasion mechanisms of exotic species. Among them, the accumulation of local pathogens hypothesis (ALPH) posits that invasive plants can accumulate local generalist pathogens that have more negative effect on native species than on themselves; as a result, invasive plants might gain competitive advantages that eventually lead to their invasion success. However, research on this topic is still quite insufficient. In this context, we performed a comprehensive literature survey in order to provide a detailed description of the origin and theoretical framework of ALPH; in addition, challenges in contemporary research such as limitations in technical methods and the complexity of interactions between plants and soil microorganisms, as well as future directions of ALPH research, are also discussed in this review. So far, there are less than ten case studies supporting ALPH; therefore, more work is needed to demonstrate whether ALPH is a suitable hypothesis to elucidate the invasion success of certain plant species.

Asymmetric succession in soil microbial communities enhances the competitive advantage of invasive alien plants

BACKGROUND

Biological invasions pose an escalating threat to native ecosystems. The accumulation of invasive alien plants worldwide is not saturated yet, underscoring the persistent and growing impact of invasions. Soil microorganisms play a key role in the process of alien plant invasion. However, the temporal dynamics of microbial communities has rarely been determined during the invasion owing to the dearth of long-term, in situ experimental systems.

RESULTS

Here, we examined the temporal succession of soil microbial communities 8 years after experiment setup in a common garden. Bacterial communities displayed divergent temporal succession, with invasive plants exhibiting higher turnover rates. Invasive alien plants reduced stochasticity in bacterial communities, likely acting as an environmental filter on community assembly. Plant growth-promoting microbes underwent higher succession rates in invasive alien plants compared to native plants, suggesting that invasive alien plants may possess a distinct advantage in fostering a favorable microbiota for their own growth and establishment. In sharp contrast, native plants selectively increased succession rates of specific plant pathogens. Furthermore, the microbial co-occurrence network was more complex in invasive plants, suggesting that invasive plants foster intricate relationships among microbial communities.

CONCLUSIONS

Therefore, the asymmetric succession in soil microbial communities enables invasive plants recruit beneficial microbiota from the surrounding soil. These results deepen our understanding of the mechanism underlying plant invasion and provide novel insights into predicting the ecological consequences resulting from widespread plant invasion. This knowledge can be incorporated into management strategies to address the evolving challenges posed by invasive plants. Video Abstract.

Early allelopathic input and later nutrient addition mediated by litter decomposition of invasive Solidago canadensis affect native plant and facilitate its invasion

Litter decomposition is essential for nutrient and chemical cycling in terrestrial ecosystems. Previous research on in situ litter decomposition has often underestimated its impact on soil nutrient dynamics and allelopathy. To address this gap, we conducted a comprehensive study involving both field and greenhouse experiments to examine the decomposition and allelopathic effects of the invasive Solidago canadensis L. in comparison with the native Phalaris arundinacea L. In the field, a 6-month litter bag experiment using leaf litter from S. canadensis and P. arundinacea was conducted across three community types: invasive, native, and mixed. Seed germination tests were also performed to investigate the allelopathic effects of decomposing litter. In the greenhouse, a pot experiment with lettuce as a bioindicator was performed to examine the allelochemical inputs from litter decomposition over various time intervals (0, 30, 60, 120, and 180 days). Subsequently, a soil-plant feedback experiment was carried out to further evaluate the effects of decomposing litter on soil biochemistry and plant dynamics. The findings of this study revealed that S. canadensis litter decomposed more rapidly and exhibited greater nitrogen (N) remaining mass compared with P. arundinacea in both single and mixed communities. After 180 days, the values for litter mass remaining for S. canadensis and P. arundinacea were 36% and 43%, respectively, when grown separately and were 32% and 44%, respectively, in mixed communities. At the invasive site, the soil ammonia and nitrate for S. canadensis increased gradually, reaching 0.89 and 14.93 mg/kg by day 120, compared with the native site with P. arundinacea. The soil organic carbon for S. canadensis at the invasive site also increased from 10.6 mg/kg on day 0 to 15.82 mg/kg on day 120, showing a higher increase than that at the native site with P. arundinacea. During the initial decomposition stages, all litters released almost all of their allelochemicals. However, at the later stages, litters continued to input nutrients into the soil, but had no significant impact on the soil carbon (C) and N cycling. Notably, litter-mediated plant-soil feedback facilitated the invasion of S. canadensis. In conclusion, this study highlights the significance of litter decomposition as a driver of transforming soil biochemistry, influencing the success of invasive S. canadensis.

Effects of alligator weed invasion on wetlands in protected areas: A case study of Lishui Jiulong National Wetland Park

Wetlands are one of the ecosystems most easily and severely invaded by alien species. Biological invasions can have significant impacts on local plant communities and ecosystem functioning. While numerous studies have assessed the impacts of biological invasions on wetlands, relatively few have been conducted in protected areas such as national wetland parks. We conducted a field survey to investigate the effects of the invasive herb Alternanthera philoxeroides (alligator weed) on the productivity and structure of plant communities and soil microbial communities in the Lishui Jiulong National Wetland Park in Zhejiang, China. We also examined the potential influence of the distance to the river edge on the impact of the alligator weed invasion. The alligator weed invasion significantly altered the plant community structure. It reduced the coverage of co-occurring plant species, including native (-31.2 %), invasive (-70.1 %), and non-invasive alien plants (-58.4 %). However, it increased species richness by 50 %, Pielou's evenness by 20 %, and Simpson's diversity index by 29.1 % for the overall plant community. Furthermore, within the community not invaded by alligator weed, increasing the distance to the river edge decreased the number of native plants by 57.0 % and the aboveground biomass of other invasive plants by 78.6 %. Contrary to expectations, no effects of the alligator weed invasion were observed on soil fungal and bacterial communities. Therefore, the impacts of the alligator weed invasion varied with spatial context and plant category, emphasizing the need to consider multiple scales and environmental factors when assessing the effects of invasive species on plant biodiversity. These insights enhance our understanding of plant invasions in wetlands and can guide the development of effective management strategies for these important ecosystems.

Chromolaena odorata affects soil nitrogen transformations and competition in tropical coral islands by altering soil ammonia oxidizing microbes

Invasive plants can change the community structure of soil ammonia-oxidizing microbes, affect the process of soil nitrogen (N) transformation, and gain a competitive advantage. However, the current researches on competition mechanism of Chromolaena odorata have not involved soil nitrogen transformation. In this study, we compared the microbially mediated soil transformations of invasive C. odorata and natives (Pisonia grandis and Scaevola taccada) of tropical coral islands. We assessed how differences in plant biomass and tissue N contents, soil nutrients, N transformation rates, microbial biomass and activity, and diversity and abundance of ammonia oxidizing microbes associated with these species impact their competitiveness. The results showed that C. odorata outcompeted both native species by allocating more proportionally biomass to aboveground parts in response to interspecific competition (12.92 % and 22.72 % more than P. grandis and S. taccada, respectively). Additionally, when C. odorata was planted with native plants, the available N and net mineralization rates in C. odorata rhizosphere soil were higher than in native plants rhizosphere soils. Higher abundance of ammonia-oxidizing bacteria in C. odorata rhizosphere soil confirmed this, being positively correlated with soil N mineralization rates and available N. Our findings help to understand the soil N acquisition and competition strategies of C. odorata, and contribute to improving evaluations and predictions of invasive plant dynamics and their ecological effects in tropical coral islands.

Elevated O3 has stronger effects than CO2 on soil nematode abundances but jointly inhibits their diversity in paddy soils

Anthropogenic activities have resulted in rising atmospheric concentrations of carbon dioxide (CO2) and ozone (O3), exerting substantial direct and indirect impacts on soil biodiversity within agroecosystems. Despite the considerable attention given to the individual impacts of elevated CO2 and O3 levels, the combined effects on soil nematode communities have not been extensively explored. In this study, we investigated the interactive effects of elevated CO2 (+200 ppm, eCO2) and O3 (+40 ppb, eO3) levels on the abundance, diversity, and trophic composition of soil nematode communities associated with two rice cultivars (Nanjing 5055, NJ5055 and Wuyujing 3, WYJ3). Our findings revealed that soil nematodes had greater abundances under eO3, whereas eCO2 had no significant impacts. Conversely, both eCO2 and eO3, and their combination led to significant reductions in nematode generic richness, accompanied by a decline in the diversity particularly associated with the WYJ3 cultivar. Moreover, eCO2 and eO3 influenced nematode community composition and environmental factors, particularly for the WYJ3 cultivar. Both eCO2 and eO3 significantly increased soil nitrate levels. The changes in nematode community composition were related to soil nitrate levels, as well as nitrogen and carbon concentrations in rice plant roots. Furthermore, interactions between eCO2 and eO3 significantly impacted soil nematode abundance and trophic composition, revealing intricate consequences for soil nematode communities that transcend predictions based on single-factor experiments. This study unveils the potential impacts posed by eCO2 and eO3 on soil biodiversity mediated by rice cultivars, plant functional characteristics and soil feedback mechanisms, thereby underscoring the complex and interactive outcomes arising from concurrent drivers of climate change within the soil food web.

Naturalized species drive functional trait shifts in plant communities

Despite decades of research documenting the consequences of naturalized and invasive plant species on ecosystem functions, our understanding of the functional underpinnings of these changes remains rudimentary. This is partially due to ineffective scaling of trait differences between native and naturalized species to whole plant communities. Working with data from over 75,000 plots and over 5,500 species from across the United States, we show that changes in the functional composition of communities associated with increasing abundance of naturalized species mirror the differences in traits between native and naturalized plants. We find that communities with greater abundance of naturalized species are more resource acquisitive aboveground and belowground, shorter, more shallowly rooted, and increasingly aligned with an independent strategy for belowground resource acquisition via thin fine roots with high specific root length. We observe shifts toward herbaceous-dominated communities but shifts within both woody and herbaceous functional groups follow community-level patterns for most traits. Patterns are remarkably similar across desert, grassland, and forest ecosystems. Our results demonstrate that the establishment and spread of naturalized species, likely in combination with underlying environmental shifts, leads to predictable and consistent changes in community-level traits that can alter ecosystem functions.

Consequences of Spiraea tomentosa invasion in Uropodina mite (Acari: Mesostigmata) communities in wet meadows

Vegetation cover has been consistently reported to be a factor influencing soil biota. Massive spreading of invasive plants may transform native plant communities, changing the quality of habitats as a result of modification of soil properties, most often having a directional effect on soil microorganisms and soil fauna. One of the most numerous microarthropods in the litter and soil is Acari. It has been shown that invasive plants usually have a negative effect on mites. We hypothesized that invasive Spiraea tomentosa affects the structure of the Uropodina community and that the abundance and species richness of Uropodina are lower in stands monodominated by S. tomentosa than in wet meadows free of this alien species. The research was carried out in wet meadows, where permanent plots were established in an invaded and uninvaded area of each meadow, soil samples were collected, soil moisture was determined and the mites were extracted. We found that Uropodina mite communities differed in the abundance of individual species but that the abundance and richness of species in their communities were similar. S. tomentosa invasion led primarily to changes in the quality of Uropodina communities, due to an increase in the shares of species from forest and hygrophilous habitats. Our results suggest that alien plant invasion does not always induce directional changes in mite assemblages, and conclude that the impact of an alien species on Uropodina may cause significant changes in the abundance and richness of individual species without causing significant changes in the abundance and diversity of their community.

Biochar alters the soil fauna functional traits and community diversity: A quantitative and cascading perspective

With the widespread use of biochar, the cascading effects of biochar exposure on soil fauna urgently require deeper understanding. A meta-analysis quantified hierarchical changes in functional traits and community diversity of soil fauna under biochar exposure. Antioxidant enzymes (24.1 %) did not fully mitigate the impact of MDA (13.5 %), leading to excessive DNA damage in soil fauna (21.2 %). Concurrently, reproduction, growth, and survival rates decreased by 20.2 %, 8.5 %, and 21.2 %, respectively. Due to a 39.7 % increase in avoidance behavior of soil fauna towards biochar, species richness ultimately increased by 80.2 %. Compared to other feeding habits, biochar posed a greater threat to the survival of herbivores. Additionally, macrofauna were the most sensitive to biochar. The response of soil fauna also depended on the type, size, concentration, and duration of biochar exposure. It should be emphasized that as exposure concentration increased, the damage to soil fauna became more severe. Furthermore, the smaller the biochar sizes, the greater the damage to soil fauna. To mitigate the adverse effects on soil fauna, this study recommens applying biochar at appropriate times and selecting large sizes in low to medium concentrations. These findings confirm the threat of biochar to soil health from the perspective of soil fauna.

Effects of plant nutrient acquisition strategies on biomass allocation patterns in wetlands along successional sequences in the semi-arid upper Yellow River basin

The ecological environment of wetlands in semi-arid regions has deteriorated, and vegetation succession has accelerated due to climate warming-induced aridification and human interference. The nutrient acquisition strategies and biomass allocation patterns reflect plant growth strategies in response to environmental changes. However, the impact of nutrient acquisition strategies on biomass allocation in successional vegetation remains unclear. We investigated 87 plant communities from 13 wetland sites in the semi-arid upper Yellow River basin. These communities were divided into three successional sequences: the herbaceous community (HC), the herbaceous-shrub mixed community (HSC), and the shrub community (SC). The nutrient composition of stems and leaves, as well as the biomass distribution above and belowground, were investigated. Results revealed that aboveground biomass increased with succession while belowground biomass decreased. Specifically, SC exhibited the highest stem biomass of 1,194.53 g m-2, while HC had the highest belowground biomass of 2,054.37 g m-2. Additionally, significant positive correlations were observed between leaf and stem biomasses in both HC and SC. The nitrogen (N) and phosphorus (P) contents within aboveground parts displayed an evident upward trend along the succession sequence. The highest N and P contents were found in SC, followed by HSC, and the lowest in HC. Stem N was negatively correlated with stem, leaf, and belowground biomass but positively correlated with root-shoot ratio. Leaf P displayed positive correlations with aboveground biomass while showing negative correlations with belowground biomass and root-shoot ratio. The ratios of C:N, C:P, and N:P in stem and leaf exhibited positive correlations with belowground biomass. The random forest model further demonstrated that stem N and leaf P exerted significant effects on aboveground biomass, while leaf P, stem N and P, and leaf C:P ratio had significant effects on belowground components. Additionally, the root-shoot ratio was significantly influenced by leaf P, leaf C:P ratio, and stem N, P, and C:P ratio. Therefore, the aboveground and belowground biomasses exhibited asynchronism across successional sequences, while plant nutrient acquisition strategies, involving nutrient levels and stoichiometric ratios, determined the biomass allocation pattern. This study offers valuable insights for assessing vegetation adaptability and formulating restoration plans in the semi-arid upper Yellow River basin.

Rhizosphere microbial community construction during the latitudinal spread of the invader Chromolaena odorata

The colonization of alien plants in new habitats is typically facilitated by microorganisms present in the soil environment. However, the diversity and structure of the archaeal, bacterial, and fungal communities in the latitudinal spread of alien plants remain unclear. In this study, the rhizosphere and bulk soil of Chromolaena odorata were collected from five latitudes in Pu' er city, Yunnan Province, followed by amplicon sequencing of the soil archaeal, bacterial, and fungal communities. Alpha and beta diversity results revealed that the richness indices and the structures of the archaeal, bacterial, and fungal communities significantly differed along the latitudinal gradient. Additionally, significant differences were observed in the bacterial Shannon index, as well as in the structures of the bacterial and fungal communities between the rhizosphere and bulk soils. Due to the small spatial scale, trends of latitudinal variation in the archaeal, bacterial, and fungal communities were not pronounced. Total potassium, total phosphorus, available nitrogen, available potassium and total nitrogen were the important driving factors affecting the soil microbial community structure. Compared with those in bulk soil, co-occurrence networks in rhizosphere microbial networks presented lower complexity but greater modularity and positive connections. Among the main functional fungi, arbuscular mycorrhizae and soil saprotrophs were more abundant in the bulk soil. The significant differences in the soil microbes between rhizosphere and bulk soils further underscore the impact of C. odorata invasion on soil environments. The significant differences in the soil microbiota along latitudinal gradients, along with specific driving factors, demonstrate distinct nutrient preferences among archaea, bacteria, and fungi and indicate complex microbial responses to soil nutrient elements following the invasion of C. odorata.

Distributions of trace elements with Long-term grazing exclusion in a semi-arid grassland of Inner Mongolia

Trace elements are the essential mineral nutrients in grassland, however, we still know little about the distributions of trace elements in grassland with long-term grazing exclusion. The contents, stocks, and proportions of iron (Fe), aluminum (Al), manganese (Mn), and boron (B) in green plant-litter-root-soil were evaluated by enclosing for 18, and 39 years inside the fence (F18 and F39) and grazing outside the fence (F0) in Inner Mongolia grassland. The results showed that F18 and F39 decreased the stocks of Fe, Al, and Mn in green plant and root compared to F0 (p < .05), while increased the stocks of them in litter (p < .05). The stock of Fe, Al, and Mn in green plant at F39 was 28.6%, 13.9%, and 39.2% higher than that at F18. The stocks of four trace elements in first layer litter at F39 were increased by 12.7%-52.2% compared to F18, whereas the stocks of them in third layer litter were decreased by 32.2%-42.5%. The F18 obviously increased the stocks of Fe and Mn in soil, especially B (p < .05). While the stocks of these trace elements in soil at F39 were 9.1%-28.0% lower than that at F18, especially B (p < .05). In conclusion, the trace elements were mainly shifted from green plant and root to soil and third layer litter with 18-year grazing exclusion. Compared to 18-year grazing exclusion, the trace elements were shifted from third layer litter and soil to root with 39-year grazing exclusion.

Microorganisms Directly Affected Sediment Carbon–Nitrogen Coupling in Two Constructed Wetlands

Clarifying the carbon–nitrogen coupling pattern in wetlands is crucial for understanding the driving mechanism of wetland carbon sequestration. However, the impacts of plants and environmental factors on the coupling of carbon–nitrogen in wetland sediments are still unclear. Sediment samples from plant (Typha angustifolia and Phragmites australis)-covered habitats and bare land were collected in two constructed wetlands in northern China. The contents of different forms of carbon and nitrogen in sediments and plants, and the sediment microbial community were detected. It was found that the sediment carbon to nitrogen (C/N) ratios did not differ significantly in the bare sites of different wetlands, but did in the plant-covered sites, which highlighted the different role of plants in shifting the carbon–nitrogen coupling in different constructed wetlands. The effects of plants on the sediment carbon–nitrogen coupling differed in two constructed wetlands, so the structural equation model was used and found that sediment microorganisms directly affected sediment C/N ratios, while water and sediment physicochemical properties indirectly affected sediment C/N ratios by altering sediment microbial functions. Multiple linear regression models showed that water pH, sediment moisture content, water dissolved oxygen, and water depth had a greater influence on the carbon metabolism potential of the sediment microbial community, while sediment moisture content had the greatest impact on the sediment microbial nitrogen metabolism potential. The study indicates that variations in environmental conditions could alter the influence of plants on the carbon and nitrogen cycles of wetland sediments. Water environmental factors mainly affect microbial carbon metabolism functions, while soil physicochemical factors, especially water content, affect microbial carbon and nitrogen metabolism functions.

Microplastics enhance the invasion of exotic submerged macrophytes by mediating plant functional traits, sediment properties, and microbial communities

Plant invasions and microplastics (MPs) have significantly altered the structure and function of aquatic habitats worldwide, resulting in severe damage to aquatic ecosystem health. However, the effects of MPs on plant invasion and the underlying mechanisms remain largely unknown. In this study, we conducted mesocosm experiments over a 90-day period to assess the effects of polystyrene microplastics on the invasion of exotic submerged macrophytes, sediment physicochemical properties, and sediment bacterial communities. Our results showed that PS-MPs significantly promoted the performance of functional traits and the invasive ability of exotic submerged macrophytes, while native plants remained unaffected. Moreover, PS-MPs addition significantly decreased sediment pH while increasing sediment carbon and nitrogen content. Additionally, MPs increased the diversity of sediment bacterial community but inhibited its structural stability, thereby impacting sediment bacterial multifunctionality to varying degrees. Importantly, we identified sediment properties, bacterial composition, and bacterial multifunctionality as key mediators that greatly enhance the invasion of exotic submerged macrophytes. These findings provide compelling evidence that the increase in MPs may exacerbate the invasion risk of exotic submerged macrophytes through multiple pathways. Overall, this study enhances our understanding of the ecological impacts of MPs on aquatic plant invasion and the health of aquatic ecosystems.

Unraveling the ecological threads: How invasive alien plants influence soil carbon dynamics

Invasive alien plants (IAPs) pose significant threats to native ecosystems and biodiversity worldwide. However, the understanding of their precise impact on soil carbon (C) dynamics in invaded ecosystems remains a crucial area of research. This review comprehensively explores the mechanisms through which IAPs influence soil C pools, fluxes, and C budgets, shedding light on their effects and broader consequences. Key mechanisms identified include changes in litter inputs, rates of organic matter decomposition, alterations in soil microbial communities, and shifts in nutrient cycling, all driving the impact of IAPs on soil C dynamics. These mechanisms affect soil C storage, turnover rates, and ecosystem functioning. Moreover, IAPs tend to increase gross primary productivity and net primary productivity leading to the alterations in fluxes and C budgets. The implications of IAP-induced alterations in soil C dynamics are significant and extend to plant-soil interactions, ecosystem structure, and biodiversity. Additionally, they have profound consequences for C sequestration, potentially impacting climate change mitigation. Restoring native plant communities, promoting soil health, and implementing species-specific management are essential measures to significantly mitigate the impacts of IAPs on soil C dynamics. Overall, understanding and mitigating the effects of IAPs on soil C storage, nutrient cycling, and related processes will contribute to the conservation of native biodiversity and complement global C neutrality efforts.

Moso bamboo (Phyllostachys edulis) expansion enhances soil pH and alters soil nutrients and microbial communities

Amid global environmental concerns, the issue of bamboo expansion has garnered significant attention due to its extensive and profound impacts on the ecosystems. Bamboo expansion occurs in native and introduced habitats worldwide, particularly in Asia. However, the effects of bamboo expansion on soil pH, nutrient levels, and microbial communities are complex and vary across different environments. To address this knowledge gap, we conducted a meta-analysis with 2037 paired observations from 81 studies. The results showed that soil pH increased by 6.99 % (0-20 cm) and 4.49 % (20-40 cm) after bamboo expansion. Notably, soil pH increased more in the coniferous forest with bamboo expansion than in the broadleaf forest. Soil pH progressively increased over time since the establishment of bamboo stands. The extent of soil pH elevation was significantly positively correlated with the proportion of bamboo within the forest stand and mean annual solar radiation. In contrast, it was significantly negatively correlated with the mean annual temperature. The elevation of pH is closely related to expansion stage and expanded forest type rather than primarily shaped by climatic factors across a large scale. We also found that bamboo expansion into coniferous forests brought about a notable 14.14 % reduction in total nitrogen (TN). Varied expansion stages resulted in TN reductions of 6.88 % and 7.99 % for mixed forests and bamboo stands, respectively, compared to native forests. Pure bamboo stands exhibited a remarkable 30.39 % increase in ammonium nitrogen and a significant 21.12 % decrease in nitrate nitrogen compared to their native counterparts. Furthermore, bamboo expansion contributed to heightened soil fungal diversity. Taken together, our findings highlight that bamboo expansion leads to an increase in soil pH and alters soil N components and fungal microbial communities, providing valuable insights for future ecological conservation and resource management.

Habitat-specific responses of soil organic matter decomposition to Spartina alterniflora invasion along China's coast

Plant invasions cause a fundamental change in soil organic matter (SOM) turnover. Disentangling the biogeographic patterns and key drivers of SOM decomposition and its temperature sensitivity (Q10 ) under plant invasion is a prerequisite for making projections of global carbon feedback. We collected soil samples along China's coast across saltmarshes to mangrove ecosystems invaded by the smooth cordgrass (Spartina alterniflora Loisel.). Microcosm experiments were carried out to determine the patterns of SOM decomposition and its thermal response. Soil microbial biomass and communities were also characterized accordingly. SOM decomposition constant dramatically decreased along the mean annual temperature gradient, whereas the cordgrass invasion retarded this change (significantly reduced slope, p < 0.05). The response of Q10 to invasion and the soil microbial quotient peaked at midlatitude saltmarshes, which can be explained by microbial metabolism strategies. Climatic variables showed strong negative controls on the Q10 , whereas dissolved carbon fraction exerted a positive influence on its spatial variance. Higher microbial diversity appeared to weaken the temperature-related response of SOM decomposition, with apparent benefits for carbon sequestration. Inconsistent responses to invasion were exhibited among habitat types, with SOM accumulation in saltmarshes but carbon loss in mangroves, which were explained, at least in part, by the SOM decomposition patterns under invasion. This study elucidates the geographic pattern of SOM decomposition and its temperature sensitivity in coastal ecosystems and underlines the importance of interactions between climate, soil, and microbiota for stabilizing SOM under plant invasion.

Leaf Extracts of Invasive Woody Species Demonstrate Allelopathic Effects on the Growth of a Lawn Grass Mixture

Biochemical composition was studied in the leaf litter of alien woody species included in the 100 most aggressive invasive species of Europe: Ailanthus altissima, Quercus rubra, Acer negundo, Robinia pseudoacacia, and Elaeagnus angustifolia. Using GC-MS, we detected 187 metabolites in the leaf litter, which are phenolic acids and their derivatives, carbohydrates and their derivatives, polyphenolic compounds, cyclic esters, glycosides, and amino acids and their derivatives. Species-specific metabolites were identified for each species. The main allelochemicals in the leaf litter extract of Q. rubra are determined mainly by the relative abundance of phenolic and fatty acids and their esters, whereas those in the leaf litter extract of R. pseudoacacia are determined by carbohydrates and their derivatives and ester of fatty acid, and those in the leaf litter extract of A. altissima are determined by glycosides. Profiles of macro- and microelements were characterized. It was found that aqueous extracts of leaf litter from all the invasive woody plants under study have a negative effect on the seed germination and initial growth of Vicia cracca and Avena strigosa used for the reclamation of disturbed urban and industrial lands. At the same time, V. cracca is potentially more sensitive.

Allelopathy-selected microbiomes mitigate chemical inhibition of plant performance

Allelopathy is a common and important stressor that shapes plant communities and can alter soil microbiomes, yet little is known about the direct effects of allelochemical addition on bacterial and fungal communities or the potential for allelochemical-selected microbiomes to mediate plant performance responses, especially in habitats naturally structured by allelopathy. Here, we present the first community-wide investigation of microbial mediation of allelochemical effects on plant performance by testing how allelopathy affects soil microbiome structure and how these microbial changes impact germination and productivity across 13 plant species. The soil microbiome exhibited significant changes to 'core' bacterial and fungal taxa, bacterial composition, abundance of functionally important bacterial and fungal taxa, and predicted bacterial functional genes after the addition of the dominant allelochemical native to this habitat. Furthermore, plant performance was mediated by the allelochemical-selected microbiome, with allelopathic inhibition of plant productivity moderately mitigated by the microbiome. Through our findings, we present a potential framework to understand the strength of plant-microbial interactions in the presence of environmental stressors, in which frequency of the ecological stress may be a key predictor of microbiome-mediation strength.

Eastern redcedar roots create legacy effects that suppresses growth of prairie species

The expansion of woody species from their historical ranges into grasslands is a global problem. Understanding the mechanisms that enable species to successfully establish and then re-encroach following their removal is critical to effectively managing problem species. Legacy effects are a mechanism that could be critical to the reestablishment of woody encroachers following their removal. Legacy effects occur when a species alters the biotic and abiotic environment in a way that affects communities that establish subsequently. In this study, we assess whether the eastern redcedar (Juniperus virginiana), a North American woody encroacher, generates legacy effects that affect communities that establish following removal of this species from an experimental grass community. We conducted a series of experiments to evaluate the effects of J. virginiana, roots on the germination and growth of grasses and to determine if the effects of root-addition treatments were derived from a microbial or allelopathic origin. Aqueous extracts of J. virginiana roots were found to inhibit the germination of grasses. We found escalating suppression of overall community biomass and the biomass of each individual species with increasing root treatments. Finally, we determined the origin of the observed suppressive effect is unlikely to be of microbial origin. Synthesis: Our results suggest that J. virginiana exudes an allelochemical into soils that inhibits the growth of certain grasses and thus has the potential to have legacy effects on future occupants. We suggest that the inhibition of the development of grasses in areas where J. virginiana has been removed is a mechanism that may favor the reestablishment of J. virginiana. Our results indicate the legacy effects of J. virginiana must be considered when conducting removal and restoration of J. virginiana infested lands.

Evaluation of the Effect of Organic Matter from Invasive Plants on Soil Nematode Communities

Invasive plants can cause loss of biodiversity and degradation of ecosystems with varying degrees of impact on soil communities. Little is known about how the organic matter of these invaders in the soil affects soil properties and nematode communities. We performed a pot experiment with non-invaded grassland soil and organic matter from two invasive plants, Fallopia japonica and Solidago gigantea, to assess and compare the composition and function of the nematode communities and soil properties. We tested five treatments: (1) non-invaded grassland soil (S), (2) 100% decayed organic matter from F. japonica (OMF), (3) 100% decayed organic matter from S. gigantea (OMS), (4) 50% soil plus 50% organic matter from F. japonica (S/OMF), and (5) 50% soil plus 50% organic matter from S. gigantea (S/OMS). Analysis of nematode composition was conducted over five months from May to September. The number of identified genera and diversity index was highest in the S treatment. The soil moisture content was highest, pH and the diversity index were lowest and herbivorous nematodes were absent in OMF and OMS treatments. The addition of OMF and OMS to soil decreased the soil pH and moisture content and increased the contents of organic carbon and total nitrogen. In S/OMF, the abundance of herbivores was lower than in S and the abundances of bacterivores and fungivores decreased during the study period. In the S/OMS, a significantly high diversity index was observed, similar to that in the S treatment. The selected ecological and functional indices differed between S/OMF, S/OMS and S, but not significantly. Our findings indicated that the organic matter from the two invasive plants could differentially contribute to interactions with nematode communities. A decrease in productivity and the slowing of nutrient cycling demonstrated by the decrease in the abundances of bacterivores and fungivorous nematodes may be common adding organic matter of invasive plants to soil. A decrease in the abundance of herbivores after the application of organic matter of F. japonica could potentially be used as an ecologically friendly management strategy against plant parasitic nematodes.

Micromorphological Sculptural Diversity in Foliar Epidermis and Trichomes Features among Invasive Species

This study examines the role of light microscopic (LM) and scanning electron microscopic (SEM) micromorphological traits of the epidermis in identifying and classifying invasive plants. SEM was conducted to increase our understanding of microscopic qualities that are not visible in light microscopy and to elucidate unclear affinities among invasive species. The study examines invasive species' morphological and anatomical characteristics from the Pothohar Plateau of Pakistan for the first time. The results showed that various micromorphological features are very useful for species' accurate identification. Adaxial and abaxial surfaces of leaves showed variations in subsidiary cells, glands, anticlinal wall patterns, stomata, and epidermal cells. Epidermal cell shapes observed were irregular, elongated, rectangular, and polygonal. Epidermal cells having maximum length were calculated in Stellaria media (126.3 μm) on adaxial side. On the abaxial surface, the minimum length was noticed in Eucalyptus camaldulensis (28.5 μm). Both glandular and nonglandular trichomes were examined, ranging from unicellular to multicellular. Most of the investigated specimens of leaves were amphistomatic, while some were hypostomatic, like Alternanthera pungens, Calotropis procera, Cannabis sativa, Lantana camara, and Thevetia peruviana. Leaf epidermal morphology contains numerous useful systematic features for accurate identifications of plant species. The micromorphological attributes under observation provide a standard criterion to the researcher for identifications of invasive flora in future morpho-taxonomic studies.

Plant invasion shifts soil microbiome and physico-chemical attributes along an elevational gradient in Kashmir Himalaya

Soil microbial communities, being situated at the interface of aboveground plant and belowground soil systems, can play a pivotal role in determining ecosystem response to the drivers of global environmental change, including invasive species. In mountains, invasive plants occurring along elevational gradients offer a unique natural experimental system to investigate the impact of invasions in determining patterns and relationships of soil microbial diversity and nutrient pools at much shorter spatial distances. Here, we studied the impact of a global plant invader, Leucanthemum vulgare, on the diversity of soil microbiome and physico-chemical attributes along an elevational gradient (1760-2880 m) in Kashmir Himalaya. We used Illumina MiSeq platform to characterize the soil microbiome in pair-wise invaded and uninvaded plots at four different sites along the gradient. We found a total of 1959 bacterial operational taxonomic units (OTUs) belonging to 152 species, and a relatively higher number of 2475 fungal OTUs belonging to 589 species. The α-diversity of soil microbiome showed a gradual increase from low to high elevation and differed significantly (p < 0.05) between the invaded and uninvaded plots. The β-diversity revealed distinct microbiome clustering among the sampling sites. Plant invasion also altered soil physico-chemical attributes along the elevational gradient. Overall, our findings suggest that the L. vulgare-induced shifts in soil microbiome and nutrient pools may be a belowground self-reinforced mechanism to facilitate its successful invasion along the elevational gradient. Our study provides new insights into invasive plant-microbe relationships with wide implications for climate warming-driven elevational range shifts in mountains.

Plant community stability is associated with a decoupling of prokaryote and fungal soil networks

Soil microbial networks play a crucial role in plant community stability. However, we lack knowledge on the network topologies associated with stability and the pathways shaping these networks. In a 13-year mesocosm experiment, we determined links between plant community stability and soil microbial networks. We found that plant communities on soil abandoned from agricultural practices 60 years prior to the experiment promoted destabilising properties and were associated with coupled prokaryote and fungal soil networks. This coupling was mediated by strong interactions of plants and microbiota with soil resource cycling. Conversely, plant communities on natural grassland soil exhibited a high stability, which was associated with decoupled prokaryote and fungal soil networks. This decoupling was mediated by a large variety of past plant community pathways shaping especially fungal networks. We conclude that plant community stability is associated with a decoupling of prokaryote and fungal soil networks and mediated by plant-soil interactions.

Tree seedling growth allocation of Castanopsis kawakamii is determined by seed-relative positions

Plants allocate growth to different organs as a strategy to obtain limiting resources in different environments. Tree seeds that fall from a mother tree settle on, within, or below the forest floor and litter layer, and their relative positions can determine seedling biomass and nutrient allocation and ultimately affect survival to the sapling stage. However, how emerged seedling biomass and nutrients of each organ are affected by seeds in different positions is not yet completely understood in subtropical forests. Therefore, an experiment was conducted with seeds positioned above the litter layers of different thicknesses, on the forest floor, and beneath the litter layer, and the influences of seed position on biomass allocation and nutrient use efficiency of emerged seedlings of Castanopsis kawakamii was examined. The aim of the study was to determine the optimal seed position to promote regeneration. Allocation strategies were well coordinated in the emerged seedlings from different seed positions. Seedlings from seeds positioned above litter layers of different thicknesses (~40 and 80 g of litter) allocated growth to leaf tissue at the expense of root tissue (lower root mass fraction) and increased nitrogen (N) and phosphorus (P) accumulation and nutrient use efficiency. Seedlings from seeds positioned beneath a deep litter layer allocated most growth to roots (high root: shoot ratio, root mass fraction) to capture available resources at the expense of leaf growth. Seedlings from seeds positioned on the forest floor allocated most growth to roots to obtain limiting resources. Further, we also found that these traits were clustered into three groups based on trait similarity, and the cumulative interpretation rate was 74.2%. Thus, seed relative positions significantly affected seedling growth by altering the allocation of resources to different organs. The different strategies indicated that root N:P ratios (entropy weight vector was 0.078) and P nutrient use efficiency were essential factors affecting seedling growth in the subtropical forest. Of the seed positions analyzed, beneath a moderate litter layer (~40 g of litter) was the most suitable position for the growth and survival of Castanopsis seedlings. In future studies, field and lab experiments will be combined to reveal the mechanisms underlying forest regeneration.

Legume effects in a native community invaded by alien Asteraceae in a multi-species comparison

Facilitation has been a long-neglected type of interaction but received more attention recently. Legumes are commonly involved in facilitative interactions due to their nitrogen fixation. Facilitative interactions are so far underappreciated yet potentially important for biological invasions, especially given increasing numbers of alien species. In a common garden experiment using 30 annual Asteraceae species (neophytes, archaeophytes, plus some natives), grown in communities with or without legume presence, we measured functional traits and fitness in focal Asteraceae, as well as nitrogen characteristics of Asteraceae and two native community phytometer species. We investigated how legume presence affects relationships between trait and nitrogen concentration and Asteraceae fitness; and whether mechanisms of facilitation in legume presence and its effects on aboveground performance differ among native phytometer, neophyte, and archaeophyte Asteraceae using the δ15N natural abundance method. Lower specific leaf area was associated with higher aboveground biomass and seed production, with a stronger effect in legume absence. Nitrogen concentration had a positive relationship with biomass, but did not generally increase seed production. Our results hint at N facilitation for the native grass phytometer Festuca rupicola when growing in legume presence, whereas the forb Potentilla argentea and 27 alien Asteraceae species did not indicate facilitative effects. Intriguingly, direct legume facilitation in native phytometer species was only detected when growing with archaeophytes neighbors, not with neophytes. This hints at varied mechanisms of competition for nitrogen between natives and alien species of different residence time and deepens the understanding of altered facilitative leguminous effects in alien species presence.

Reduced Antibiotic Resistance in the Rhizosphere of Lupinus albus in Mercury-Contaminated Soil Mediated by the Addition of PGPB

The emergence of antibiotic resistance (AR) poses a threat to the "One Health" approach. Likewise, mercury (Hg) pollution is a serious environmental and public health problem. Its ability to biomagnify through trophic levels induces numerous pathologies in humans. As well, it is known that Hg-resistance genes and AR genes are co-selected. The use of plant-growth-promoting bacteria (PGPB) can improve plant adaptation, decontamination of toxic compounds and control of AR dispersal. The cenoantibiogram, a technique that allows estimating the minimum inhibitory concentration (MIC) of a microbial community, has been postulated as a tool to effectively evaluate the evolution of a soil. The present study uses the metagenomics of 16S rRNA gene amplicons to understand the distribution of the microbial soil community prior to bacterial inoculation, and the cenoantibiogram technique to evaluate the ability of four PGPB and their consortia to minimize antibiotic resistance in the rhizosphere of Lupinus albus var. Orden Dorado grown in Hg-contaminated soils. Results showed that the addition of A1 strain (Brevibacterium frigoritolerans) and its consortia with A2, B1 and B2 strains reduced the edaphic community´s MIC against cephalosporins, ertapenem and tigecycline. The metagenomic study revealed that the high MIC of non-inoculated soils could be explained by the bacteria which belong to the detected taxa,. showing a high prevalence of Proteobacteria, Cyanobacteria and Actinobacteria.

The Invasive Tradescantia zebrina Affects Litter Decomposition, but It Does Not Change the Lignocellulolytic Fungal Community in the Atlantic Forest, Brazil

Invasive plants affect ecosystems across various scales. In particular, they affect the quality and quantity of litter, which influences the composition of decomposing (lignocellulolytic) fungal communities. However, the relationship among the quality of invasive litter, lignocellulolytic cultivated fungal community composition, and litter decomposition rates under invasive conditions is still unknown. We evaluated whether the invasive herbaceous Tradescantia zebrina affects the litter decomposition in the Atlantic Forest and the lignocellulolytic cultivated fungal community composition. We placed litter bags with litter from the invader and native plants in invaded and non-invaded areas, as well as under controlled conditions. We evaluated the lignocellulolytic fungal communities by culture method and molecular identification. Litter from T. zebrina decomposed faster than litter from native species. However, the invasion of T. zebrina did not alter decomposition rates of either litter type. Although the lignocellulolytic fungal community composition changed over decomposition time, neither the invasion of T. zebrina nor litter type influenced lignocellulolytic fungal communities. We believe that the high plant richness in the Atlantic Forest enables a highly diversified and stable decomposing biota formed in conditions of high plant diversity. This diversified fungal community is capable of interacting with different litter types under different environmental conditions.

Seasonality and assembly of soil microbial communities in coastal salt marshes invaded by a perennial grass

Plant invasion profoundly changes the microbial-driven processes in the ecosystem; however, the seasonality of soil microbial communities and their assembly under plant invasion is poorly understood. In this study, coastal salt marshes with native Suaeda salsa (L.) Pall. and exotic Spartina alterniflora Loisel. in the Yellow River Estuary, North China, were selected, and soil bacterial and fungal communities and their seasonal variance were characterized by metabarcoding sequencing of the 16S rRNA gene and ITS2 regions, respectively. The importance of deterministic and stochastic processes in shaping bacterial and fungal seasonal assembly was explored by the null model. Results showed that soil microbes exhibited the lowest diversities in spring, while their diversity significantly improved in summer and autumn with the increase in organic carbon and nitrogen content in soils. Strong seasonal variances in microbial communities were observed, but plant invasion reduced the seasonal variation strength of soil bacteria. For the microbial assembly, the seasonal variability of soil bacterial community was mainly controlled by homogeneous selection, whereas soil fungal community was dominantly structured by stochastic processes. Among the selected variables, soil pH was the key abiotic factor driving the seasonal changes in bacteria and fungi. The microbial function annotation derived from taxonomy-based inference suggested that carbon metabolism was relatively stronger in spring, but nitrogen and sulfur metabolism increased evidently in summer and autumn, and the proportion of saprophytic fungi increased substantially after plant invasion. The seasonal turnover of bacterial and fungal groups were tightly associated with the seasonal variation in soil carbon and nitrogen contents. Collectively, these findings reveal the strong seasonal variability of different soil microbial constituents in plant-invaded coastal salt marshes and suggest the linkage between microbial community assembly and microbial-mediated functions in the context of plant invasions.

Hydrogen cyanide, a key plant defense, as a potential driver of root-associated nematode communities along urbanization gradients

Introduction

Plant chemical defenses can influence the distribution, community composition, and abundance of soil biota. Urbanization plays a key role in shaping soil biotic communities either directly through changes in soil properties or indirectly via changes in plant characteristics such as defense traits. The effects of urbanization and plant defenses on the abundance and structure of aboveground plant-associated communities have been studied, yet their effects on belowground root-associated communities are poorly understood.

Methods

Here we sampled white clover (Trifolium repens L.) leaves and roots along urban–rural gradients in the cities of Antwerp and Ghent, Belgium. We measured production of hydrogen cyanide (HCN) in leaves, a known defense trait against herbivores, and abundances of different feeding guilds of nematodes associated with the roots.

Results

We found that HCN production decreased with increasing levels of urbanization in both cities. Urbanization was significantly correlated with shifts in root-associated nematode community structure in Antwerp but not in Ghent. Responses of nematode feeding guilds and trophic groups to urbanization were highly dependent on the clovers’ HCN production, especially in Ghent. Changes in nematode channel ratio in Antwerp indicated that urban root-associated nematode communities of white clover were more strongly dominated by fungivorous nematodes.

Discussion

Our results demonstrate that urbanization is driving changes in a plant phenotypic trait and in the community structure of root-associated nematodes, as well as that both changes interact. Plant defense mechanisms could thus help elucidate the effects of urbanization on root-associated biota communities. As strong differences existed between the two studied cities, the particular properties of cities should be taken into account to better understand the direction and strength of phenotypic trait changes driven by urbanization.

Nitrate Nitrogen and pH Correlate with Changes in Rhizosphere Microbial Community Assemblages during Invasion of Ambrosia artemisiifolia and Bidens pilosa

The rhizosphere of invasive plants presumably develops different soil microbial assemblages compared with native plants, which may hinder or promote their invasion. However, to date, no studies have clearly explored rhizosphere microbial community assemblages during invasion. The invasive species Ambrosia artemisiifolia L. and Bidens pilosa L. are widely distributed in China and are known to reduce local biodiversity and cause agricultural losses. Monoculture of A. artemisiifolia or B. pilosa, a mixture of each invasive and native species, and monoculture of native species were established to simulate different degrees of invasion. Metagenomic sequencing techniques were used to test microbial community structure and function. The aim was to explore the drivers of the assembly of peculiar functional microbes in the rhizosphere soil of invasive species during the long-term invasive-native species interaction. Compared with the native species, the relative abundance of 34 microbial genera was higher in the rhizosphere soil of the invasive species. The NO₃-N concentration in the rhizosphere soil from the A. artemisiifolia and B. pilosa monocultures was lower than that from monocultures of the three native plants, whereas pH followed the opposite trend. The NO₃-N concentration was significantly and negatively correlated with Sporichthya, Afipia, Actinokineospora, and Pseudolabrys. pH was positively correlated with Bradyrhizobium, Actinoplanes, Micromonospora, Steroidobacter, Burkholderia, and Labilithrix. The differences in soil microbes, NO₃-N concentrations, and pH between native and invasive species suggest that the rhizosphere soil microbial assemblages may vary. The reduced NO₃-N concentration and increased pH corelated with changes in rhizosphere microbial community during A. artemisiifolia and B. pilosa invasion. IMPORTANCE Soil microbial communities play a vital role in the growth of invasive plants. Invasive species may shape peculiar functional microbes in the rhizosphere soil of an invasive species to benefit its growth. However, the drivers of the assembly of soil microbial communities in the rhizosphere soil of invasive species remain unclear. Our study established the relationship between soil microbial communities and soil chemical properties during invasion by A. artemisiifolia and B. pilosa. Additionally, it showed that the presence of the invasive plants correlated with changes in NO₃-N and pH, as well as in rhizosphere microbial community assemblage. Furthermore, the study provided important insights into the difference in the microbial community assembly between native and invasive plant species.

Drought reduces invasive grass performance by disrupting plant-microbe interactions that enhance plant nitrogen supply

Non-native invasive plants can promote their dominance in novel ecosystems by accelerating soil nutrient cycling via interactions with decomposer microbes. Changes in abiotic conditions associated with frequent or prolonged drought may disrupt these interactions, but the effects of disruption on invasive plant performance and the underpinning mechanisms are poorly understood. Here, we used rainout shelters in an experimental field setting to test the hypothesis that drought reduces invasive plant performance by reducing microbial metabolic activity, resulting in decreased nitrogen flow to plants. We imposed growing season drought on populations of the exotic grass Microstegium vimineum, a widespread invasive plant in eastern deciduous forests, and quantified effects on aboveground and belowground biomass, and carbon (C) and nitrogen (N) cycling among plants, decomposers, and soil. Drought resulted in a 24% decrease in soil respiration, a 16% decrease in phenol oxidase enzyme activity, a 12% decrease in dissolved organic N concentration, and a decrease in the C:N ratio of particulate organic matter, suggesting reduced microbial metabolic activity and nutrient mining of soil organic matter. Drought also reduced aboveground Microstegium biomass 33% and increased Microstegium leaf C:N ratio, consistent with a decline in plant N uptake. We conclude that drought can reduce the performance of existing invasive species populations by suppressing plant-microbe interactions that increase nitrogen supply to plants, which may have consequences for the persistence of invasive plants under hydrologic change.

Evidence of plant-soil feedback in South Texas grasslands associated with invasive Guinea grass

Plant-soil feedback (PSF) processes play an integral role in structuring plant communities. In native grasslands, PSF has a largely negative or stabilizing effect on plant growth contributing to species coexistence and succession, but perturbations to a system can alter PSF, leading to long-term changes. Through changes to soil abiotic and biotic properties, invasion by non-native plants has a strong impact on belowground processes with broad shifts in historical PSFs. Guinea grass, Megathyrsus maximus, an emerging invasive in South Texas, can efficiently exclude native plants in part due to its fast growth rate and high biomass accumulation, but its impacts on belowground processes are unknown. Here, we provide a first look at PSF processes in South Texas savannas currently undergoing invasion by Guinea grass. In this pilot study, we addressed the question of how the presence of the invasive M. maximus may alter PSF compared to uninvaded grasslands. Under greenhouse conditions, we assessed germination and growth of Guinea grass and the seed bank in soil collected from grasslands invaded and uninvaded by Guinea grass. We found that Guinea grass grown in soil from invaded grasslands grew taller and accumulated higher biomass than in soil from uninvaded grasslands. Plants grown from the seed bank were more species rich and abundant in soil from uninvaded grasslands but had higher biomass in soil from invaded grasslands. In South Texas savannas, we found evidence to support shifts in the direction of PSF processes in the presence of Guinea grass with positive feedback processes appearing to reinforce invasion and negative feedback processes possibly contributing to species coexistence in uninvaded grasslands. Future work is needed to determine the mechanisms behind the observed shifts in PSF and further explore the role PSF has in Guinea grass invasion.

Parasitism Shifts the Effects of Native Soil Microbes on the Growth of the Invasive Plant Alternanthera philoxeroides

Soil microbes play an important role in plant invasion, and parasitic plants regulate the growth of invasive plants. However, the mechanisms by which parasitic plants regulate the effects of soil microbes on invasive plants have not been investigated. Here, we used the invasive plant Alternanthera philoxeroides and the holoparasitic plant Cuscuta grovonii to test whether and how C. grovonii parasitism shifts the effect of native soil microbes on the growth of A. philoxeroides. In a factorial setup, A. philoxeroides was grown in pots with the presence versus absence of parasitism and the presence versus absence of native soil microbes. The findings showed that native soil microbes increased the biomass and clonal growth of A. philoxeroides only in the absence of a parasite, whereas parasitism decreased the biomass and clonal growth of A. philoxeroides only in the presence of soil microbes. In addition, the presence of soil microbes increased the deleterious effects of the parasite on A. philoxeroides. These results indicate that parasitism can shift the effects of native soil microbes on the growth of the invasive plant A. philoxeroides. Our results enrich the understanding of the mechanisms underlying the success of plant invasion.

Plant Species-Driven Distribution of Individual Clades of Comammox Nitrospira in a Subtropical Estuarine Wetland

Plant species play a crucial role in mediating the activity and community structure of soil microbiomes through differential inputs of litter and rhizosphere exudates, but we have a poor understanding of how plant species influence comammox Nitrospira, a newly discovered ammonia oxidizer with pivotal functionality. Here, we investigate the abundance, diversity, and community structure of comammox Nitrospira underneath five plant species and a bare tidal flat at three soil depths in a subtropical estuarine wetland. Plant species played a critical role in driving the distribution of individual clades of comammox Nitrospira, explaining 59.3% of the variation of community structure. Clade A.1 was widely detected in all samples, while clades A.2.1, A.2.2, A.3 and B showed plant species-dependent distribution patterns. Compared with the native species Cyperus malaccensis, the invasion of Spartina alterniflora increased the network complexity and changed the community structure of comammox Nitrospira, while the invasive effects from Kandelia obovata and Phragmites australis were relatively weak. Soil depths significantly influenced the community structure of comammox Nitrospira, but the effect was much weaker than that from plant species. Altogether, our results highlight the previously unrecognized critical role of plant species in driving the distribution of comammox Nitrospira in a subtropical estuarine wetland.

Moso bamboo (Phyllostachys edulis (Carrière) J. Houzeau) invasion affects soil microbial communities in adjacent planted forests in the Lijiang River basin, China

Introduction

Moso bamboo (Phyllostachys edulis (Carrière) J. Houz.), the most widely distributed economic bamboo species in southern China, can easily invade adjacent communities due to its clonal reproduction. However, there is little information on the effects of its establishment and expansion to adjacent forest soil communities, particularly in planted forests.

Methods

We investigated the relationships between soil properties and the microbial community during bamboo invasion under different slope directions (shady or sunny slope) and positions (bottom, middle, or top slope), in three typical stand types (bottom: pure moso bamboo, middle: mixed stands of moso bamboo and Masson pine (Pinus massoniana Lamb.), and top: pure Masson pine) in the Lijiang River Basin. This study aimed to explore the effects of key environmental factors on soil microbial composition, diversity, and abundance.

Results and Discussion

The results showed that the abundance of Acidobacteria bacterium and Acidobacteria bacterium 13_2_20CM_58_27, and Verrucomicrobia bacterium decreased as the slope increased (p < 0.05), whereas the abundance of Alphaproteobacteria bacterium, Actinobacteria bacterium, Trebonia kvetii, and Bradyrhizobium erythrophlei increased as the slope increased (p < 0.05). However, the difference of slope direction on microbial communities was not significant. The pH, organic matter (OM) and total phosphorus (TP) were the key soil environmental factors; most microorganisms (Betaproteobacteria bacterium, Candidatus Eisenbacteria bacterium, Betaproteobacteria bacterium SCGC_AG - 212 - J23, Gemmatimonadetes bacterium, Actinobacteria bacterium 13_2_20CM_2_66_6, and Myxococcaceae bacterium) showed a positive relationship with pH and a negative relationship with OM and TP. Slope position significantly affected OM, calcium (Ca), total nitrogen (TN), available phosphorus (AP), hydrolyzed nitrogen (HN), pH, and microbial abundance and composition. Slope direction significantly affected TP and magnesium (Mg). The structural equations also indicated that slope position had an effect on microbial composition, abundance, and diversity. Slope position was negatively correlated with pH (r = -0.333, p = 0.034) and positively correlated with OM (r = 0.728, p < 0.001), TN (r = 0.538, p < 0.001) and Ca (r = 0.672, p < 0.001); pH was positively correlated with microbial composition (r = 0.634, p < 0.001), abundance (r = 0.553, p < 0.001) and diversity (r = 0.412, p = 0.002), TN was positively correlated with microbial composition (r = 0.220, p = 0.014) and abundance (r = 0.206, p = 0.013), and Ca was negatively correlated with microbial composition (r = -0.358, p = 0.003) and abundance (r = -0.317, p = 0.003). Slope position can also influence microbial composition (r = 0.452, p < 0.001) directly. In addition, slope direction had an indirect effect on microbial diversity through total potassium (TK). Therefore, we proposed that the different variations in microbial community during bamboo invasion could be related to the influence of invasion on the soil properties at different invasion stages.

Effects of Invasive Plant Diversity on Soil Microbial Communities

Native plant communities can be invaded by different numbers of alien plant species or by the same number of alien plant species with different levels of evenness. However, little is known about how alien invasive plant species richness and evenness affect soil microbial communities. We constructed native herbaceous plant communities invaded by exotic plants with different richness (1, 2, 4 and 8 species) and evenness (high and low) and analyzed soil physico-chemical properties and the diversity and composition of soil fungal and bacterial communities by high-throughput Illumina sequencing. Overall, the species richness and evenness of invasive plants had no significant effect on bacterial and fungal alpha diversity (OTUs, Shannon, Simpson, Chao1 and ACE) or the soil physico-chemical properties. However, invasive species richness had a significant impact on the relative abundance of the most dominant fungi, Ascomycota and Bipolaris, and the dominant bacteria, Actinobacteriota, which increased with increasing invasive species richness. The relative abundance of the dominant microbial groups was significantly correlated with the relative abundance of some specific invasive plants in the community. This study sheds new light on the effects of plant co-invasion on soil microbial communities, which may help us understand the underlying mechanisms of multiple alien plant invasion processes from the perspective of soil microorganisms.

Bacteria common to rhizosphere communities of Asiatic bittersweet across a post-glacial landscape

Invasive plants such as Asiatic bittersweet (Celastrus orbiculatus Thunb.) are a significant problem for land managers as they impact plant species composition, disrupt nutrient dynamics and structure of native ecosystems, and are difficult to eradicate. As a result of the increasing abundance of Asiatic bittersweet across the eastern U.S., we have been investigating underlying factors potentially contributing to the success of this plant. Recently, ecologists have been investigating the role of plant-soil-microbe interactions contributing to plant invasion. This work has led to question: are there certain microbes (e.g., bacteria, fungi) contributing to the success of some invasive plants? We hypothesize that despite differences in geologic age of soils where Asiatic bittersweet has established in the Indiana Dunes National Park there are sufficient common factors that led to common bacterial taxa in their rhizosphere. The objectives were to determine differences and commonalities in the soil chemistry, plant community and bacterial communities of Asiatic bittersweet plants. To achieve these objectives, bittersweet plants were collected at thirteen locations in the national park from soils ranging in geologic age from 150 to over 14,500 years. Surrounding soil chemistry, plant cover and the 16S rRNA gene amplicon sequences of rhizosphere soil bacterial communities of these Asiatic bittersweet were compared. Asiatic bittersweet coverage of sampling sites ranged from 2 to 77% averaging 52 ± 2%. There were statistically significant differences (p &lt; 0.05) in alpha diversity (Shannon, Faith’s PD and Pielou’s evenness) and beta diversity (Bray Curtis, Jaccard, unweighted Unifrac, weighted Unifrac) among the samples when grouped by soil age or habitat. Despite these differences in the bacterial communities from different soil ages and habitats, some bacterial taxa (e.g., Bacillus, Streptomyces, Sphingomonas and Rhizobiales) previously found in other studies to be beneficial to plant growth were found in every rhizosphere community sampled. These microbes provide insight into a possible contributing factor to the success of this invasive plant at the Indiana Dunes National Park, and a strategy for future work to reduce the impact of Asiatic bittersweet establishment and offer some new strategies to manage this nuisance species.

Distribution and management of Fallopia japonica in riparian biotopes in Slovakia and Austria

Globally, invasive species represent a serious threat to biodiversity and to the ecosystem. As an undesirable part of riparian ecosystems, invasive plants form continuous growths on the banks of watercourses. One of the biggest problems at river bank sites is Japanese knotweed, Fallopia japonica (Houtt.) Ronse Decr, which is an extremely invasive and aggressive weed. The topic of the interaction of flow and invasive plant species in shore stands is rich and presents a wide range of possibilities for research. The presented paper brings the results of our studies on the invasions of F. japonica in chosen riparian vegetation sites in Austria and Slovakia from 2011–2020 (36 stands). Our research was aimed at the survey on the changes in the distribution (spread) of F. japonica at the selected river sites; assessment of the impact of the watercourse regime on the spread of F. japonica; monitoring of the population growth dynamics of F. japonica and assessment of possibilities for effective eradication of F. japonica in context of the riparian vegetation management. We used standard techniques of field survey, mapping, flow modeling/simulation, and laboratory experiments. Our research results showed that water streams are not primary invasion starters until there is a flood. As long as flooding does not exceed the critical speed of the water stream, there is no direct damage to the invasive plant. The water body can be a secondary trigger for plant invasion at normal speeds. In addition, F. japonica reproduction ability directly conditions its population dynamic growth. We can report that selective invasion removal adapted to local conditions can be most suitable and beneficial for municipalities.

Stronger mutualistic interactions with arbuscular mycorrhizal fungi help Asteraceae invaders outcompete the phylogenetically related natives

Mutualistic interactions with arbuscular mycorrhizal fungi (AMF) greatly affect the outcome of plant-plant competition, especially for invasive plants competing against native plants. We examined the effects of AMF on the competition between invasive Asteraceae plants and the phylogenetically related native plants. We compared the performance of seven invasive Asteraceae plants from different genera with that of their phylogenetically related native counterparts in response to AMF in monocultures and mixed cultures. We investigated how interactions with AMF impact the competition between Asteraceae relatives. Total biomass increased with AMF colonization in both invasive and native plants. Arbuscular mycorrhizal fungi improved the competitiveness of invasive plants, but decreased that of native plants. Competition increased the shoot nitrogen, phosphorus and root myristic acid concentrations and relative expression of fatty acid transporter genes (RiFAT1 and RiFAT2) in AMF-colonized invasive plants, but decreased those in AMF-colonized native plants. Structural equation models indicated that the presence of AMF increased the uptake of phosphorus, but not nitrogen, by invasive plants, which probably provided more myristic acids to symbiotic AMF in return. These results suggest that invasive Asteraceae plants have greater mutualistic interactions with AMF than their phylogenetically related native counterparts, potentially contributing to invasion success.

Mapping the Distribution and Dispersal Risks of the Alien Invasive Plant Ageratina adenophora in China

Identifying the distribution dynamics of invasive alien species can help in the early detection of and rapid response to these invasive species in newly invaded sites. Ageratina adenophora, a worldwide invasive plant, has spread rapidly since its invasion in China in the 1940s, causing serious damage to the local socioeconomic and ecological environment. To better control the spread of this invasive plant, we used the MaxEnt model and ArcGIS based on field survey data and online databases to simulate and predict the spatial and temporal distribution patterns and risk areas for the spread of this species in China, and thus examined the key factors responsible for this weed’s spread. The results showed that the risk areas for the invasion of A. adenophora in the current period were 18.394° N–33.653° N and 91.099° E–121.756° E, mainly in the tropical and subtropical regions of China, and densely distributed along rivers and well-developed roads. The high-risk areas are mainly located in the basins of the Lancang, Jinsha, Yalong, and Anning Rivers. With global climate change, the trend of continued invasion of A. adenophora is more evident, with further expansion of the dispersal zone towards the northeast and coastal areas in all climatic scenarios, and a slight contraction in the Yunnan–Guizhou plateau. Temperature, precipitation, altitude, and human activity are key factors in shaping the distribution pattern of A. adenophora. This weed prefers to grow in warm and precipitation-rich environments such as plains, hills, and mountains; in addition, increasing human activities provide more opportunities for its invasion, and well-developed water systems and roads can facilitate its spread. Measures should be taken to prevent its spread into these risk areas.

Exploring plant volatile-mediated interactions between native and introduced plants and insects

In invasion scenarios, native and introduced species co-occur creating new interactions and modifying existing ones. Many plant–plant and plant–insect interactions are mediated by volatile organic compounds (VOCs), however, these have seldom been studied in an invasion context. To fill this knowledge gap, we explored some interactions mediated by VOCs between native and introduced plants and insects in a New Zealand system. We investigated whether a native plant, Leptospermum scoparium (mānuka), changes its volatile profile when grown adjacent to two European introduced plants, Calluna vulgaris (heather) and Cytisus scoparius (Scotch broom), in a semi-field trial using potted plants without above- or below-ground physical contact. We also investigated the influence of plant cues on the host-searching behaviour of two beetles, the native Pyronota festiva (mānuka beetle), and the introduced biocontrol agent Lochmaea suturalis (heather beetle), by offering them their host-plant and non-host volatiles versus clean air, and their combination in a Y-tube olfactometer. As a follow-up, we performed preference/feeding tests in Petri dishes with fresh plant material. Results of the semi-field experiment show a significant reduction in green leaf volatiles, sesquiterpenes and total volatile emissions by mānuka plants neighbouring heather. In the Y-tube assays, the native beetle P. festiva performed poorly in discriminating between host and non-host plants based on plant volatile cues only. However, it performed relatively well in the Petri dish tests, where other cues (i.e., visual, gustatory or tactile) were present. In contrast, the introduced beetle L. suturalis showed high host-specificity in both Y-tube and Petri dish assays. This study illustrates the importance of VOCs in mediating interactions between introduced and native species, suggesting that invasive plants can disrupt native plants’ communication and affect the host-searching behaviour of native insects. It also reinforces the relevance of regular host testing on introduced weed biocontrol agents to avoid unwanted host shifts or host-range expansion.

Misleading estimates of economic impacts of biological invasions: Including the costs but not the benefits

The economic costs of non-indigenous species (NIS) are a key factor for the allocation of efforts and resources to eradicate or control baneful invasions. Their assessments are challenging, but most suffer from major flaws. Among the most important are the following: (1) the inclusion of actual damage costs together with various ancillary expenditures which may or may not be indicative of the real economic damage due to NIS; (2) the inclusion of the costs of unnecessary or counterproductive control initiatives; (3) the inclusion of controversial NIS-related costs whose economic impacts are questionable; (4) the assessment of the negative impacts only, ignoring the positive ones that most NIS have on the economy, either directly or through their ecosystem services. Such estimates necessarily arrive at negative and often highly inflated values, do not reflect the net damage and economic losses due to NIS, and can significantly misguide management and resource allocation decisions. We recommend an approach based on holistic costs and benefits that are assessed using likely scenarios and their counter-factual.

Biogeographic Patterns of Leaf Element Stoichiometry of Stellera chamaejasme L. in Degraded Grasslands on Inner Mongolia Plateau and Qinghai-Tibetan Plateau

Plant leaf stoichiometry reflects its adaptation to the environment. Leaf stoichiometry variations across different environments have been extensively studied in grassland plants, but little is known about intraspecific leaf stoichiometry, especially for widely distributed species, such as Stellera chamaejasme L. We present the first study on the leaf stoichiometry of S. chamaejasme and evaluate its relationships with environmental variables. S. chamaejasme leaf and soil samples from 29 invaded sites in the two plateaus of distinct environments [the Inner Mongolian Plateau (IM) and Qinghai-Tibet Plateau (QT)] in Northern China were collected. Leaf C, N, P, and K and their stoichiometric ratios, and soil physicochemical properties were determined and compared with climate information from each sampling site. The results showed that mean leaf C, N, P, and K concentrations were 498.60, 19.95, 2.15, and 6.57 g kg⁻¹; the average C:N, C:P, N:P, N:K and K:P ratios were 25.20, 245.57, 9.81, 3.13, and 3.21, respectively. The N:P:K-ratios in S. chamaejasme leaf might imply that its growth is restricted by K- or K+N. Moreover, the soil physicochemical properties in the S. chamaejasme-infested areas varied remarkably, and few significant correlations between S. chamaejasme leaf ecological stoichiometry and soil physicochemical properties were observed. These indicate the nutrient concentrations and stoichiometry of S. chamaejasme tend to be insensitive to variations in the soil nutrient availability, resulting in their broad distributions in China’s grasslands. Besides, different homeostasis strength of the C, N, K, and their ratios in S. chamaejasme leaves across all sites were observed, which means S. chamaejasme could be more conservative in their use of nutrients improving their adaptation to diverse conditions. Moreover, the leaf C and N contents of S. chamaejasm were unaffected by any climate factors. However, the correlation between leaf P content and climate factors was significant only in IM, while the leaf K happened to be significant in QT. Besides, MAP or MAT contribution was stronger in the leaf elements than soil by using mixed effects models, which illustrated once more the relatively weak effect of the soil physicochemical properties on the leaf elements. Finally, partial least squares path modeling suggested that leaf P or K contents were affected by different mechanisms in QT and IM regions, suggesting that S. chamaejasme can adapt to changing environments by adjusting its relationships with the climate or soil factors to improve its survival opportunities in degraded grasslands.

The Effects of Fire Disturbance on Litter Decomposition and C:N:P Stoichiometry in a Larix gmelinii Forest Ecosystem of Boreal China

Fire disturbance can affect the function of the boreal forest ecosystem through litter decomposition and nutrient element return. In this study, we selected the Larix gmelinii forest, a typical forest ecosystem in boreal China, to explore the effect of different years (3 years, 9 years, 28 years) after high burn severity fire disturbance on the decomposition rate (k) of leaf litter and the Carbon:Nitrogen:Phosphorus (C:N:P) stoichiometry characteristics. Our results indicated that compared with the unburned control stands, the k increased by 91–109% within 9 years after fire disturbance, but 28 years after fire disturbance the decomposition rate of the upper litter decreased by 45% compared with the unburned control stands. After fire disturbance, litter decomposition in boreal forests can be promoted in the short term (e.g., 9 years after a fire) and inhibited in the long term (e.g., 28 years after a fire). Changes in litter nutrient elements caused by the effect of fire disturbance on litter decomposition and on the C, N, and C:N of litter were the main litter stoichiometry factors for litter decomposition 28 years after fire disturbance. The findings of this research characterize the long-term dynamic change of litter decomposition in the boreal forest ecosystem, providing data and theoretical support for further exploring the relationship between fire and litter decomposition.