Evidence for biological denitrification inhibition (BDI) by plant secondary metabolites

From winery by-product to soil improver? - A comprehensive review of grape pomace in agriculture and its effects on soil properties and functions

Grape pomace (GP), a by-product of winemaking, is rich in organic carbon and nutrients, offering potential as an alternative to synthetic soil amendments. However, its broader use in agriculture remains limited due to uncertainties about long-term environmental and agronomic impacts. This review assesses the potential of GP as a soil amendment, highlighting its ability to enhance soil organic matter, nutrient availability, and soil physicochemical properties. At the same time, concerns remain regarding its acidic nature, wide carbon-to‑nitrogen (C/N) ratio, and bioactive compounds, such as mycotoxins and (poly)phenols, which could negatively impact soil microbial communities and nutrient cycling. Furthermore, residual contaminants such as pesticides and heavy metals in GP may pose ecotoxicological risks, potentially disrupting soil ecosystem functions and contaminating surrounding environments. Besides these challenges, research on the efficiency, fate and mobility of GP in soil, particularly in relation to soil type, climate, and agricultural practices, is limited. Furthermore, the effects of various (pre)treatments (e.g., composting, fermentation) on GP properties and soil interactions require more systematic investigation. Future research should focus on long-term field trials, advanced analytical methods, and effective monitoring frameworks. It is essential to refine regulatory guidance based on comprehensive risk assessments to ensure safe application and maximize GP's agronomic and environmental benefits. Overcoming these challenges could transform GP into a valuable resource for sustainable agriculture, contributing to soil health, climate resilience, and a circular economy.

Plants mitigate ecosystem nitrous oxide emissions primarily through reductions in soil nitrate content: Evidence from a meta-analysis

Nitrous oxide (N2O) is a potent greenhouse gas (GHG) and an ozone-depleting substance. The presence of plants in an ecosystem can either increase or decrease N2O emissions, or play a negligible role in driving N2O emissions. Here, we conducted a meta-analysis comparing ecosystem N2O emissions from planted and unplanted systems to evaluate how plant presence influences N2O emissions and examined the mechanisms driving observed responses. Our results indicate that plant presence reduces N2O emissions while it increases dinitrogen (N2) emissions from ecosystems through decreases in soil nitrate concentration as well as increases in complete denitrification and mineral N immobilization. The response of N2O emissions to plant presence was universal across major terrestrial ecosystems - including forests, grassland and cropland - and it did not vary with N fertilization. Further, in light of the potential mechanisms of N2O formation in plant cells, we discussed how plant presence could enhance the emission of N2O from plants themselves. Improving our understanding of the mechanisms driving N2O emissions in response to plant presence could be beneficial for enhancing the robustness for predictions of our GHG sinks and sources and for developing strategies to minimize emissions at the ecosystem scale.

Tipping the plant-microbe competition for nitrogen in agricultural soils

Nitrogen (N) is the most limiting nutrient in agroecosystems, and its indiscriminate application is at the center of the environmental challenges facing agriculture. To solve this dilemma, crops' nitrogen use efficiency (NUE) needs to increase - in other words, more of the applied nitrogen needs to reach humans. Microbes are the key to cracking this problem. Microbes use nitrogen as an energy source, an electron acceptor, or incorporate it in their biomass. These activities change the form and availability of nitrogen for crops' uptake, impacting its NUE, yields and produce quality. Plants (and microbes) have, however, evolved many mechanisms to compete for soil nitrogen. Understanding and harnessing these competitive mechanisms would enable us to tip the nitrogen balance to the advantage of crops. We will review these competitive mechanisms and highlight some approaches that were applied to reduce microbial competition for N in an agricultural context.

Can plants build their niche through modulation of soil microbial activities linked with nitrogen cycling? A test with Arabidopsis thaliana

In natural systems, different plant species have been shown to modulate specific nitrogen (N) cycling processes so as to meet their N demand, thereby potentially influencing their own niche. This phenomenon might go beyond plant interactions with symbiotic microorganisms and affect the much less explored plant interactions with free-living microorganisms involved in soil N cycling, such as nitrifiers and denitrifiers. Here, we investigated variability in the modulation of soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), and their ratio (NEA : DEA), across 193 Arabidopsis thaliana accessions. We studied the genetic and environmental determinants of such plant-soil interactions, and effects on plant biomass production in the next generation. We found that NEA, DEA, and NEA : DEA varied c. 30-, 15- and 60-fold, respectively, among A. thaliana genotypes and were related to genes linked with stress response, flowering, and nitrate nutrition, as well as to soil parameters at the geographic origin of the analysed genotypes. Moreover, plant-mediated N cycling activities correlated with the aboveground biomass of next-generation plants in home vs away nonautoclaved soil, suggesting a transgenerational impact of soil biotic conditioning on plant performance. Altogether, these findings suggest that nutrient-based plant niche construction may be much more widespread than previously thought.

The critical role of a conserved lysine residue in periplasmic nitrate reductase catalyzed reactions

Periplasmic nitrate reductase NapA from Campylobacter jejuni (C. jejuni) contains a molybdenum cofactor (Moco) and a 4Fe-4S cluster and catalyzes the reduction of nitrate to nitrite. The reducing equivalent required for the catalysis is transferred from NapC → NapB → NapA. The electron transfer from NapB to NapA occurs through the 4Fe-4S cluster in NapA. C. jejuni NapA has a conserved lysine (K79) between the Mo-cofactor and the 4Fe-4S cluster. K79 forms H-bonding interactions with the 4Fe-4S cluster and connects the latter with the Moco via an H-bonding network. Thus, it is conceivable that K79 could play an important role in the intramolecular electron transfer and the catalytic activity of NapA. In the present study, we show that the mutation of K79 to Ala leads to an almost complete loss of activity, suggesting its role in catalytic activity. The inhibition of C. jejuni NapA by cyanide, thiocyanate, and azide has also been investigated. The inhibition studies indicate that cyanide inhibits NapA in a non-competitive manner, while thiocyanate and azide inhibit NapA in an uncompetitive manner. Neither inhibition mechanism involves direct binding of the inhibitor to the Mo-center. These results have been discussed in the context of the loss of catalytic activity of NapA K79A variant and a possible anion binding site in NapA has been proposed.

Biological mitigation of soil nitrous oxide emissions by plant metabolites

Plant metabolites significantly affect soil nitrogen (N) cycling, but their influence on nitrous oxide (N2O) emissions has not been quantitatively analyzed on a global scale. We conduct a comprehensive meta-analysis of 173 observations from 42 articles to evaluate global patterns of and principal factors controlling N2O emissions in the presence of root exudates and extracts. Overall, plant metabolites promoted soil N2O emissions by about 10%. However, the effects of plant metabolites on N2O emissions from soils varied with experimental conditions and properties of both metabolites and soils. Primary metabolites, such as sugars, amino acids, and organic acids, strongly stimulated soil N2O emissions, by an average of 79%, while secondary metabolites, such as phenolics, terpenoids, and flavonoids, often characterized as both biological nitrification inhibitors (BNIs) and biological denitrification inhibitors (BDIs), reduced soil N2O emissions by an average of 41%. The emission mitigation effects of BNIs/BDIs were closely associated with soil texture and pH, increasing with increasing soil clay content and soil pH on acidic and neutral soils, and with decreasing soil pH on alkaline soils. We furthermore present soil incubation experiments that show that three secondary metabolite types act as BNIs to reduce N2O emissions by 32%-45%, while three primary metabolite classes possess a stimulatory effect of 56%-63%, confirming the results of the meta-analysis. Our results highlight the potential role and application range of specific secondary metabolites in biomitigation of global N2O emissions and provide new biological parameters for N2O emission models that should help improve the accuracy of model predictions.

Biological inhibition of denitrification (BDI): an early plant strategy for Fallopia × bohemica seedling development

BACKGROUND AND AIMS

The successful plant Fallopia × bohemica presents interesting capacities for control of the soil nitrogen cycle at the adult stage, termed biological inhibition of denitrification (BDI). The BDI strategy allows the plant, via the production of secondary metabolites (procyanidins), to compete with the denitrifying microbial community and to divert nitrate from the soil for its benefit. In this study, we analysed whether seedlings of F. × bohemica can implement BDI at the seedling stage. We also determined whether soil nitrogen availability influences the implementation of BDI and seedling growth.

METHODS

We sowed achenes of F. × bohemica in soils representing a nitrogen gradient (six treatments) and harvested seedlings after 20 or 40 days of growth. The denitrification and related microbial communities (i.e. functional gene abundances of nirK and nirS), soil parameters (nitrate content and humidity) and plant performance (biomass, growth and root morphology) were determined.

KEY RESULTS

On soil without addition of nitrogen, BDI was observed after 20 days of growth, whereas a stimulation of denitrification was found after 40 days. The increase of soil N content had few effects on the activity and structure of the soil denitrifying community and on the plant biomasses or the relative growth rates. Correlations between plant and microbial parameters were observed after 20 days of growth, reflecting early and strong chemical interactions between plants and the denitrifying community, which decreased with plant growth after 40 days.

CONCLUSIONS

This study shows that an early BDI enhances the efficiency of nitrogen acquisition in the first weeks of growth, allowing for a conservative root strategy after 40 days. This switch to a conservative strategy involved resource storage, an altered allocation to above- and below-ground parts and an investment in fine roots. It now seems clear that this storage strategy starts at a very young age with early establishment of BDI, giving this clonal plant exceptional capacities for storage and multiplication.

An integrated metagenomic, metabolomic and transcriptomic survey of Populus across genotypes and environments

Bridging molecular information to ecosystem-level processes would provide the capacity to understand system vulnerability and, potentially, a means for assessing ecosystem health. Here, we present an integrated dataset containing environmental and metagenomic information from plant-associated microbial communities, plant transcriptomics, plant and soil metabolomics, and soil chemistry and activity characterization measurements derived from the model tree species Populus trichocarpa. Soil, rhizosphere, root endosphere, and leaf samples were collected from 27 different P. trichocarpa genotypes grown in two different environments leading to an integrated dataset of 318 metagenomes, 98 plant transcriptomes, and 314 metabolomic profiles that are supported by diverse soil measurements. This expansive dataset will provide insights into causal linkages that relate genomic features and molecular level events to system-level properties and their environmental influences.

Nitrogen-loss and carbon-footprint reduction by plant-rhizosphere exudates

Low-carbon approaches to agriculture constitute a pivotal measure to address the challenge of global climate change. In agroecosystems, rhizosphere exudates are significantly involved in regulating the nitrogen (N) cycle and facilitating belowground chemical communication between plants and soil microbes to reduce direct and indirect emissions of greenhouse gases (GHGs) and control N runoff from cultivated sites into natural water bodies. Here, we discuss specific rhizosphere exudates from plants and microorganisms and the mechanisms by which they reduce N loss and subsequent N pollution in terrestrial and aquatic environments, including biological nitrification inhibitors (BNIs), biological denitrification inhibitors (BDIs), and biological denitrification promoters (BDPs). We also highlight promising application scenarios and challenges in relation to rhizosphere exudates in terrestrial and aquatic environments.

Cereals rhizosphere microbiome undergoes host selection of nitrogen cycle guilds correlated to crop productivity

Sustainable transformation of agricultural plant production requires the reduction of nitrogen (N) fertilizer application. Such a reduced N fertilizer application may impede crop production due to an altered symbiosis of crops and their rhizosphere microbiome, since reduced N input may affect the competition and synergisms with the plant. The assessment of such changes in the crop microbiome functionalities at spatial scales relevant for agricultural management remains challenging. We investigated in a field plot experiment how and if the N cycling guilds of the rhizosphere of globally relevant cereal crops - winter barley, wheat and rye - are influenced by reduced N fertilization. Crop productivity was assessed by remote sensing of the shoot biomass. Microbial N cycling guilds were investigated by metagenomics targeting diazotrophs, nitrifiers, denitrifiers and the dissimilatory nitrate to ammonium reducing guild (DNRA). The functional composition of microbial N cycling guilds was explained by crop productivity parameters and soil pH, and diverged substantially between the crop species. The responses of individual microbial N cycling guild abundances to shoot dry weight and rhizosphere nitrate content was modulated by the N fertilization treatments and the crop species, which was identified based on regression analyses. Thus, characteristic shifts in the microbial N cycling guild acquisition associated with the crop host species were resolved. Particularly, the rhizosphere of rye was enriched with potentially N-preserving microbial guilds - diazotrophs and the DNRA guild - when no fertilizer was applied. We speculate that the acquisition of microbial N cycling guilds was the result of plant species-specific acquisition strategies. Thus, the investigated cereal crop holobionts have likely different symbiotic strategies that make them differently resilient against reduced N fertilizer inputs. Furthermore, we demonstrated that these belowground patterns of N cycling guilds from the rhizosphere microbiome are linked to remotely sensed aboveground plant productivity.

Plant development alters the nitrogen cycle in subsurface flow constructed wetlands: Implications to the strategies for intensified treatment performance

Plant development greatly influences the composition structure and functions of microbial community in constructed wetlands (CWs) via plant root activities. However, our knowledge of the effect of plant development on microbial nitrogen (N) cycle is poorly understood. Here, we investigated the N removal performance and microbial structure in subsurface flow CWs at three time points corresponding to distinct stages of plant development: seedling, mature and wilting. Overall, the water parameters were profoundly affected by plant development with the increased root activities including radial oxygen loss (ROL) and root exudates (REs). The removal efficiency of NH4+-N was significantly highest at the mature stage (p < 0.01), while the removal performance of NO3--N at the seedling stage. The highest relative abundances of nitrification- and anammox-related microbes (Nitrospira, Nitrosomonas, and Candidatus Brocadia, etc.) and functional genes (Amo, Hdh, and Hzs) were observed in CWs at the mature stage, which can be attributed to the enhanced intensity of ROL, creating micro-habitat with high DO concentration. On the other hand, the highest relative abundances of denitrification- and DNRA-related microbes (Petrimonas, Geobacter, and Pseudomonas, etc.) and functional genes (Nxr, Nir, and Nar, etc.) were observed in CWs at the seedling and wilting stages, which can be explained by the absence of ROL and biological denitrification inhibitor derived from REs. Results give insights into microbial N cycle in CWs with different stages of plant development. More importantly, a potential solution for intensified N removal via the combination of practical operation and natural regulation is proposed.

Secondary metabolites responses of plants exposed to ozone: an update

Tropospheric ozone (O3) is a secondary pollutant that causes oxidative stress in plants due to the generation of excess reactive oxygen species (ROS). Phenylpropanoid metabolism is induced as a usual response to stress in plants, and induction of key enzyme activities and accumulation of secondary metabolites occur, upon O3 exposure to provide resistance or tolerance. The phenylpropanoid, isoprenoid, and alkaloid pathways are the major secondary metabolic pathways from which plant defense metabolites emerge. Chronic exposure to O3 significantly accelerates the direction of carbon flows toward secondary metabolic pathways, resulting in a resource shift in favor of the synthesis of secondary products. Furthermore, since different cellular compartments have different levels of ROS sensitivity and metabolite sets, intracellular compartmentation of secondary antioxidative metabolites may play a role in O3-induced ROS detoxification. Plants' responses to resource partitioning often result in a trade-off between growth and defense under O3 stress. These metabolic adjustments help the plants to cope with the stress as well as for achieving new homeostasis. In this review, we discuss secondary metabolic pathways in response to O3 in plant species including crops, trees, and medicinal plants; and how the presence of this stressor affects their role as ROS scavengers and structural defense. Furthermore, we discussed how O3 affects key physiological traits in plants, foliar chemistry, and volatile emission, which affects plant-plant competition (allelopathy), and plant-insect interactions, along with an emphasis on soil dynamics, which affect the composition of soil communities via changing root exudation, litter decomposition, and other related processes.

Manure-derived hydrochar superior to manure: Reducing non-point pollution risk by altering nitrogen and phosphorus fugacity in the soil-water system

Hydrothermal carbonization (HTC) technology is an emerging technology for the disposal of manure-based wet wastes. However, the effects of manure-derived hydrochar inputs to agricultural soils on nitrogen (N) and phosphorus (P) morphology and conversion in soil-water systems remain largely unexplored. In this study, pig and cattle manure (PM and CM), and their derived hydrochar (PCs and CCs) were applied to agricultural soils, with changes in nutrient morphology and enzyme activities related to N and P transformation in the soil-water systems observed through flooded incubation experiments. The results showed that floodwater ammonia N concentrations were reduced by 12.9-29.6% for PCs relative to PM, and 21.6-36.9% for CCs relative to CM, respectively. Moreover, floodwater total P concentrations of PCs and CCs were reduced by 11.7-20.7% relative to PM and CM. Soil enzyme activities closely related to N and P transformations in the soil-water system responded differently to manure and manure-derived hydrochar application. Compared to manure, the application of manure-derived hydrochar inhibited soil urease and acid phosphatase activity by up to 59.4% and 20.3%, respectively, whereas it had significant promotion effects on soil nitrate reductase (∼69.7%) and soil nitrite reductase (∼64.0%). The products of manure after HTC treatments have the characteristics of organic fertilizers, and the fertilization effects of PCs are more prominent than CCs, which are subject to further verification in field trials. Our findings improve the current understanding of manure-derived organic matter affecting N and P conversions in soil-water systems and the risk for non-point source pollution.

Multifarious Responses of Forest Soil Microbial Community Toward Climate Change

Forest soils are a pressing subject of worldwide research owing to the several roles of forests such as carbon sinks. Currently, the living soil ecosystem has become dreadful as a consequence of several anthropogenic activities including climate change. Climate change continues to transform the living soil ecosystem as well as the soil microbiome of planet Earth. The majority of studies have aimed to decipher the role of forest soil bacteria and fungi to understand and predict the impact of climate change on soil microbiome community structure and their ecosystem in the environment. In forest soils, microorganisms live in diverse habitats with specific behavior, comprising bulk soil, rhizosphere, litter, and deadwood habitats, where their communities are influenced by biotic interactions and nutrient accessibility. Soil microbiome also drives multiple crucial steps in the nutrient biogeochemical cycles (carbon, nitrogen, phosphorous, and sulfur cycles). Soil microbes help in the nitrogen cycle through nitrogen fixation during the nitrogen cycle and maintain the concentration of nitrogen in the atmosphere. Soil microorganisms in forest soils respond to various effects of climate change, for instance, global warming, elevated level of CO2, drought, anthropogenic nitrogen deposition, increased precipitation, and flood. As the major burning issue of the globe, researchers are facing the major challenges to study soil microbiome. This review sheds light on the current scenario of knowledge about the effect of climate change on living soil ecosystems in various climate-sensitive soil ecosystems and the consequences for vegetation-soil-climate feedbacks.

Plant Secondary Metabolites: The Weapons for Biotic Stress Management

The rise in global temperature also favors the multiplication of pests and pathogens, which calls into question global food security. Plants have developed special coping mechanisms since they are sessile and lack an immune system. These mechanisms use a variety of secondary metabolites as weapons to avoid obstacles, adapt to their changing environment, and survive in less-than-ideal circumstances. Plant secondary metabolites include phenolic compounds, alkaloids, glycosides, and terpenoids, which are stored in specialized structures such as latex, trichomes, resin ducts, etc. Secondary metabolites help the plants to be safe from biotic stressors, either by repelling them or attracting their enemies, or exerting toxic effects on them. Modern omics technologies enable the elucidation of the structural and functional properties of these metabolites along with their biosynthesis. A better understanding of the enzymatic regulations and molecular mechanisms aids in the exploitation of secondary metabolites in modern pest management approaches such as biopesticides and integrated pest management. The current review provides an overview of the major plant secondary metabolites that play significant roles in enhancing biotic stress tolerance. It examines their involvement in both indirect and direct defense mechanisms, as well as their storage within plant tissues. Additionally, this review explores the importance of metabolomics approaches in elucidating the significance of secondary metabolites in biotic stress tolerance. The application of metabolic engineering in breeding for biotic stress resistance is discussed, along with the exploitation of secondary metabolites for sustainable pest management.

Fallopia japonica and Impatiens glandulifera are colonized by species-poor root-associated fungal communities but have minor impacts on soil properties in riparian habitats

Fallopia japonica and Impatiens glandulifera are major plant invaders on a global scale that often become dominant in riparian areas. However, little is known about how these species affect interactions in soil–plant systems. The aim of this study was to investigate the impact of both species on abiotic and biotic soil properties, with a special focus on fungi. We investigated eight sites along small streams invaded by F. japonica and I. glandulifera, respectively, and compared each with nearby sites dominated by the native species Urtica dioica. Three different types of samples were collected: bulk soil, rhizosphere soil and roots from invasive and native stands at each site. Bulk soil samples were analysed for soil physicochemical, microbial properties (soil microbial respiration and ergosterol) and soil arthropod abundance (Acari and Collembola). Soil respiration was also evaluated in rhizosphere samples. The fungal community composition of both bulk soil and roots were analysed using a metabarcoding approach. Soil physicochemical properties as well as soil microbial activity, fungal biomass and soil fungal operational unit taxonomic unit (OTU) richness did not differ between invaded and native riparian habitats, indicating only minor belowground impacts of the two invasive plant species. Soil microbial activity, fungal biomass and soil fungal OTU richness were rather related to the soil physicochemical properties. In contrast, Acari abundance decreased by 68% in the presence of F. japonica, while Collembola abundance increased by 11% in I. glandulifera sites. Moreover, root-associated fungal communities differed between the invasive and native plants. In F. japonica roots, fungal OTU richness of all investigated ecological groups (mycorrhiza, endophytes, parasites, saprobes) were lower compared to U. dioica. However, in I. glandulifera roots only the OTU richness of mycorrhiza and saprobic fungi was lower. Overall, our findings show that F. japonica and I. glandulifera can influence the abundance of soil arthropods and are characterized by lower OTU richness of root-associated fungi.

Relationships between denitrification rates and functional gene abundance in a wetland: The roles of single- and multiple-species plant communities

Wetland soil denitrification removes excess inorganic nitrogen (N) and prevents eutrophication in aquatic ecosystems. Wetland plants have been considered the key factors determining the capacity of wetland soil denitrification to remove N pollutants in aquatic ecosystems. However, the influences of various plant communities on wetland soil denitrification remain unknown. In the present study, we measured variations in soil denitrification under different herbaceous plant communities including single Phragmites karka (PK), single Paspalum thunbergia (PT), single Zizania latifolia (ZL), a mixture of Paspalum thunbergia plus Phragmites karka (PTPK), a mixture of Paspalum thunbergia plus Zizania latifolia (PTZL), and bare soil (CK) in the Estuary of Nantiaoxi River, the largest tributary of Qingshan Lake in Hangzhou, China. The soil denitrification rate was significantly higher in the surface (0-10 cm) than the subsurface (10-20 cm) layer. Wetland plant growth increased the soil denitrification rate by significantly increasing the soil water content, nitrate concentration, and ln(nirS) + ln(nirK). A structural equation model (SEM) showed that wetland plants indirectly regulated soil denitrification by altering the aboveground and belowground plant biomass, nitrate concentration, abundances of denitrifying functional genes, and denitrification potential. There was no significant difference in soil denitrification rates among PT, PK and ZL. The soil denitrification rate was significantly lower in PTZL than PTPK. Two-plant communities did not necessarily enhance the denitrification rate compared to single planting, the former had a greater competitiveness on N uptake and consequently reduced the amount of nitrate available for denitrification. As PTPK had the highest denitrification rate, co-planting P. thunbergia and P. karka could effectively improve N removal efficiency and help mitigate eutrophication in adjacent aquatic ecosystems. The results of this investigation provide useful information guiding the selection of appropriate wetland herbaceous plant species for wetland construction and the removal of N pollutants in aquatic ecosystems.

Micromanaging the nitrogen cycle in agroecosystems

While large inputs of synthetic nitrogen fertilizers enable our current rate of crop production and feed a growing global population, these fertilizers come at a heavy environmental cost. Driven by microbial processes, excess applied nitrogen is lost from agroecosystems as nitrate and nitrous oxide (N₂O) contaminating aquatic ecosystems and contributing to climate change. Interest in nitrogen-fixing microorganisms as an alternative to synthetic fertilizers is rapidly accelerating. Microbial inoculants offer the promise of a sustainable and affordable source of nitrogen, but the impact of inoculants on nitrogen dynamics at an ecosystem level is not fully understood. This review synthesizes recent studies on microbial inoculants as tools for nutrient management and considers the ramifications of inoculants for nitrogen transformations beyond fixation.

Root exudates enhanced rhizobacteria complexity and microbial carbon metabolism of toxic plants

Root exudates and rhizosphere microorganisms play key roles in the colonization of toxic plants under climate change and land degradation. However, how root exudates affect the rhizosphere microorganisms and soil nutrients of toxic plants in degraded grasslands remains unknown. We compared the interaction of soil microbial communities, root exudates, microbial carbon metabolism, and environmental factors in the rhizosphere of toxic and non-toxic plants. Deterministic processes had a greater effect on toxic than non-toxic plants, as root exudates affected rhizosphere microorganisms directly. The 328 up-regulated compounds in root exudates of toxic plants affected the diversity of rhizosphere microorganisms. Rhizosphere bacteria-enriched enzymes were involved in the phenylpropanoid biosynthesis pathway. Root exudates of toxic plants form complex networks of rhizosphere microorganisms, provide high rhizosphere nutrients, and increase microbial carbon metabolism. The interaction between root exudates and rhizosphere microorganisms is the key mechanism that enables toxic plants to spread in degraded grassland habitats.

Impacts of slurry application methods and inhibitors on gaseous emissions and N2O pathways in meadow-cinnamon soil

This study aimed to evaluate the impact of mitigation practices (slurry application methods and inhibitors applications) on gas emissions and identify the soil N₂O production pathways in cattle slurry applied soil using isotopocule mapping approach. First, we compared the NH₃ and N₂O emissions of cattle slurry applied soil in a summer maize field experiment in north China plain (NCP) with four treatments: control (CK, no fertilization), slurry application using surface (SA-S), slurry application using band application (BA-S), and chemical fertilizer application using band application (BA-C). Then, an incubation experiment was conducted to investigate the mitigation effect of nitrification inhibitors (dicyandiamide, DCD) and denitrification inhibitors (procyanidins, PC) and their combination (DCD + PC) on gaseous N emissions with slurry applied using incorporation (IA) or surface application (SA) methods. The results showed that the total gaseous N emissions (N₂O-N and NH₃-N) in field were in the order of SA-S (1534 mg m^-2) > BA-S (338 mg m^-2) > BA-C (128 mg m^-2) > CK (55 mg m^-2), and the dominant N loss contributor varied from NH₃ in SA-S (∼89%) to N₂O in BA-S (∼94%) and BA-C (∼88%). Moreover, the isotopocule mapping approach indicated that emitted N₂O of the slurry applied soil in field appeared to have lower r_N2O values and led to more N₂O + N₂ emissions at the initial fertilization period. The incubation experiment indicated that the N₂O emissions of slurry-applied soil were significantly reduced by DCD (∼45%) and DCD + PC (∼67%) application in comparison with CK (p < 0.05), and the stronger contributions of bacterial denitrification/nitrifier denitrification to N₂O production were revealed by the lower δ¹⁵N^SP in N₂O using the isotopocule mapping approach. In conclusion, in NCP the gaseous losses of the slurry applied field can be largely reduced by using incorporation method, and greater reduction could be achieved given the simultaneous application of nitrification/denitrification inhibitors.

The Prediction of Distribution of the Invasive Fallopia Taxa in Slovakia

Invasive species are now considered the second biggest threat for biodiversity and have adverse environmental, economic and social impacts. Understanding its spatial distribution and dynamics is crucial for the development of tools for large-scale mapping, monitoring and management. The aim of this study was to predict the distribution of invasive Fallopia taxa in Slovakia and to identify the most important predictors of spreading of these species. We designed models of species distribution for invasive species of Fallopia—Fallopia japonica—Japanese knotweed, Fallopia sachalinensis—Sakhalin knotweed and their hybrid Fallopia × bohemica—Czech knotweed. We designed 12 models—generalized linear model (GLM), generalized additive model (GAM), classification and regression trees (CART), boosted regression trees (BRT), multivariate adaptive regression spline (MARS), random forests (RF), support vector machine (SVM), artificial neural networks (ANN), maximum entropy (Maxent), penalized maximum likelihood GLM (GLMNET), domain, and radial basis function network (RBF). The accuracy of the models was evaluated using occurrence data for the presence and absence of species. The final simplified logistic regression model showed the three most important prediction variables lead by distances from roads and rails, then type of soil and distances from water bodies. The probability of invasive Fallopia species occurrence was evaluated using Pearson’s chi-squared test (χ21). It significantly decreases with increasing distance from transport lines (χ21 = 118.85, p < 0.001) and depends on soil type (χ21 = 49.56, p < 0.001) and the distance from the water, where increasing the distance decrease the probability (χ21 = 8.95, p = 0.003).

Herbaceous plant species support soil microbial performance in deciduous temperate forests

Although herbaceous plant layer may contribute significantly to plant diversity and nutrient turnover, its effects on the soil environment in forest ecosystems remain largely unexplored. In this study, we compared the effects of mono-dominant and multi-species assemblages of herb plants on soil physicochemical and microbial properties in two temperate deciduous (beech and riparian) forests. We hypothesized that the presence of herbaceous plants would increase microbial activity and biomass, and nutrient availability in soil when compared to bare soil. This increase would be the highest in multi-species assemblages as high plant diversity supports microbial performance and soil processes, and the expected patterns would be essentially similar in both forests. Allium ursinum L. and Dentaria enneaphyllos L. represented herb species forming mono-dominant patches in beech forest, while Aegopodium podagraria L. and Ficaria verna Huds. represented herb species forming mono-dominant patches in riparian forest. Our hypotheses were only partly supported by the data. We found that herb plant species affected soil microbial communities and processes, particularly in the riparian forest, but they generally did not influence soil physicochemical properties. In the beech forest, herbaceous plants increased saprotrophic fungi biomass, fungi/bacteria ratio, and arylsulfatase activity, with the highest values under D. enneaphyllos. In the riparian forest, a number of microbial parameters, namely bacteria, G+ bacteria, and saprotrophic fungi biomass, fungi/bacteria ratio, and soil respiration exhibited the lowest values in bare soil and the highest values in soil under A. podagraria. Contrary to expectations, soils under multi-species assemblages were characterized by intermediate values of microbial parameters. Concluding, herbaceous plant species largely supported soil microbial communities in deciduous temperate forests but did not affect soil chemical properties. The potential reasons for the positive influence of herb plants on soil microbes (litterfall, rhizodeposition) require further investigation.

The inhibitory efficacy of procyanidin on soil denitrification varies with N fertilizer type applied

Denitrification is a major process of the nitrogen (N) cycle by converting nitrate (NO₃^-) back to gaseous nitrogen (N₂), which leads to massive losses of N, including fertilizer N, from agricultural systems. One mitigation strategy for these N losses involves denitrification inhibition by plant-derived biological denitrification inhibitors (BDIs). Procyanidin was recently identified as a new class of BDI in root extracts from Fallopia spp. However, the efficacy of this compound on soil denitrification under different N fertilizer sources is not well understood. Here, a 14-day microcosm experiment was conducted using three nitrate-based fertilizers (NH₄NO₃, KNO₃, and Ca(NO₃)₂) to investigate the impact of procyanidin on soil denitrification and associated microbial pathways. Results showed that procyanidin inhibited denitrification activity regardless of the source of N fertilizer applied, but the inhibitory efficacy of procyanidin varied with N fertilizer types. Addition of procyanidin had greater denitrification inhibition in the soils applied with NH₄NO₃ than with other types of N fertilizer. Moreover, nitrate reductase activity was significantly suppressed by procyanidin addition across all three N fertilizers tested. Quantification of denitrifying functional genes (nirS, nirK, and nosZ) demonstrated that procyanidin inhibited the activity and growth of nirS- and nirK-type denitrifiers, but stimulated the growth of nosZI-containing denitrifiers. These findings indicate that the inhibition of soil denitrification by procyanidin was mainly a result of the suppression of nitrate reductase activity and nirS- and nirK-type denitrifiers abundance. The use of procyanidin together with N fertilizers, especially NH₄NO₃, can be an effective way to reduce the N losses by denitrification.

Root exudates impact plant performance under abiotic stress

Plant root exudates serve pivotal roles in supporting plant development and interactions with the physicochemical and biological factors in the rhizosphere. Under stress conditions, root exudation is involved in enhancing plant resource-use efficiency and facilitating the crosstalk between plant and soil microbes to ameliorate stress. Although there are a large number of root exudates that remain to be characterized, recent technological advancements have allowed for the function of many exudate compounds to be elucidated. In this review, we discuss current knowledge about the key root exudates that modulate plant resource-use efficiency under various abiotic stresses including drought, aluminum toxicity, phosphorus, nitrogen, and iron deficiency. The role that key root exudates play in shaping microbial communities in the rhizosphere under stress conditions is also an important consideration addressed in this review.

A review of root exudates and rhizosphere microbiome for crop production

Increasing crop yields and ensuring food security is a major global challenge. In order to increase crop production, chemical fertilizers and pesticides are excessively used. However, the significance of root exudates is understudied. Beneficial interactions between plant and rhizosphere microbiome are critical for plant fitness and health. In this review, we discuss the application and progress of current research methods and technologies in terms of root exudates and rhizosphere microbiome. We summarize how root exudates promote plant access to nitrogen, phosphorus, and iron, and how root exudates strengthen plant immunity to cope with biotic stress by regulating the rhizosphere microbiome, and thereby reducing dependence on fertilizers and pesticides. Optimizing these interactions to increase plant nutrient uptake and resistance to biotic stresses offers one of the few untapped opportunities to confront sustainability issues in food security. To overcome the limitations of current research, combination of multi-omics, imaging technology together with synthetic communities has the potential to uncover the interaction mechanisms and to fill the knowledge gap for their applications in agriculture to achieve sustainable development.

Effects of the Denitrification Inhibitor "Procyanidins" on the Diversity, Interactions, and Potential Functions of Rhizosphere-Associated Microbiome

Some plant secondary metabolites, such as procyanidins, have been demonstrated to cause biological denitrification inhibition (BDI) of denitrifiers in soils concomitantly with a gain in plant biomass. The present work evaluated whether procyanidins had an impact on the diversity of nontarget microbial communities that are probably involved in soil fertility and ecosystem services. Lettuce plants were grown in two contrasting soils, namely Manziat (a loamy sand soil) and Serail (a sandy clay loam soil) with and without procyanidin amendment. Microbial diversity was assessed using Illumina sequencing of prokaryotic 16S rRNA gene and fungal ITS regions. We used a functional inference to evaluate the putative microbial functions present in both soils and reconstructed the microbial interaction network. The results showed a segregation of soil microbiomes present in Serail and Manziat that were dependent on specific soil edaphic variables. For example, Deltaproteobacteria was related to total nitrogen content in Manziat, while Leotiomycetes and Firmicutes were linked to Ca2+ in Serail. Procyanidin amendment did not affect the diversity and putative activity of microbial communities. In contrast, microbial interactions differed according to procyanidin amendment, with the results showing an enrichment of Entotheonellaeota and Mucoromycota in Serail soil and of Dependentiae and Rozellomycetes in Manziat soil.

Invasive plant Reynoutria japonica produces large amounts of phenolic compounds and reduces the biomass but not activity of soil microbial communities

Reynoutria japonica is one of the most invasive plant species. Its success in new habitats may be associated with the release of secondary metabolites. The aim of this study was to compare phenolic concentrations in plant biomass and soils between plots with R. japonica and resident plants (control), and determine the effects of these compounds on soil microbial communities. Samples of plant shoots and rhizomes/roots, and soil were collected from 25 paired plots in fallow and riparian habitats in Poland. We measured concentrations of total phenolics, condensed tannins, catechin, chlorogenic acid, emodin, epicatechin, hyperoside, physcion, piceatannol, polydatin, procyanidin B3, quercetin, resveratrol, and resveratroloside. Soil microbial parameters were represented by acid and alkaline phosphomonoesterases, β-glucosidase, phenoloxidase, and peroxidase activity, culturable bacteria activity and functional diversity measured with Biolog Ecoplates, and microbial biomass and community structure measured with phospholipid fatty acid (PLFA) analysis. We found that concentrations of total phenolics and condensed tannins were very high in R. japonica leaves and rhizomes/roots, and concentrations of most phenolic compounds were very high in R. japonica rhizomes/roots when compared to resident plant species. Concentrations of most phenolics in mineral soil did not differ between R. japonica and control plots; the only exceptions were catechin and resveratrol which were higher and lower, respectively, under the invader. Total microbial and bacterial (G+, G-) biomass was decreased by approx. 30% and fungal biomass by approx. 25% in invaded soils in comparison to control. Among soil functional microbial parameters, only peroxidase activity and functional diversity differed between R. japonica and resident plant plots; peroxidase activity was higher, while functional diversity was lower in soil under R. japonica. The negative effects of R. japonica on microbial biomass may be related to catechin or its polymers (proanthocyanidins) or to other phenolics contained in high concentrations in R. japonica rhizomes.

Biochemical and Genetic Approaches Improving Nitrogen Use Efficiency in Cereal Crops: A Review

Nitrogen is an essential nutrient required in large quantities for the proper growth and development of plants. Nitrogen is the most limiting macronutrient for crop production in most of the world's agricultural areas. The dynamic nature of nitrogen and its tendency to lose soil and environment systems create a unique and challenging environment for its proper management. Exploiting genetic diversity, developing nutrient efficient novel varieties with better agronomy and crop management practices combined with improved crop genetics have been significant factors behind increased crop production. In this review, we highlight the various biochemical, genetic factors and the regulatory mechanisms controlling the plant nitrogen economy necessary for reducing fertilizer cost and improving nitrogen use efficiency while maintaining an acceptable grain yield.

Responses of the species complex Fallopia × bohemica to single-metal contaminations to Cd, Cr or Zn: growth traits, metal accumulation and secondary metabolism

Plant responses to heavy metals and their storage constitute a crucial step to understand the environmental impacts of metallic trace elements (MTEs). In controlled experiments, we previously demonstrated the tolerance and resilience of Japanese knotweed to soil artificial polymetallic contamination. Using the same experimental design, we tested here the effect of three individual MTEs on Fallopia × bohemica performance traits. Rhizome fragments from three different sites (considered as distinct morphotypes) were grown in a greenhouse for 1 month on a prairial soil artificially contaminated with either Cd, Cr (VI) or Zn at concentrations corresponding to relatively highly polluted soils. Our results confirmed the high tolerance of Bohemian knotweed to metal stress, though, plant response to MTE pollution was dependant on MTE identity. Bohemian knotweed was stimulated by Cr (VI) (increased root and aerial masses), did not display any measurable change in performance traits under Cd at the high dose of 10 mg kg^-1, and uptook all MTEs in its rhizome, but only Zn was transferred to its aerial parts. We also highlighted changes in root secondary metabolism that were more accentuated with Zn, including the increase of anthraquinone, stilbene and biphenyl derivatives. These results compared to multi-contamination experiments previously published suggest complex interactions between metals and plant, depending principally on metal identity and also suggest a potential role of soil microbes in the interactions.

Microbial indicators are better predictors of wheat yield and quality than N fertilization

In view of their key roles in many soil- and plant-related processes, we hypothesized that soil microorganisms could play a larger role in determining wheat baking quality than nitrogen fertilization. A field experiment was conducted under bread wheat production conditions, where different fertilization treatments, ranging from 0-120 kg/ha NH4NO3, were applied. Soil samples were taken in May, June and July. Functional genes in the nitrogen cycle were quantified and amplicons of the 16S rRNA gene and the ITS region were sequenced. Wheat yields were measured, and the grain baking quality was analysed for each plot. Fertilisation did not significantly influence the yields and the grain quality. Many bacterial and fungal Amplicon Sequence Variants showed significant positive or negative correlations with yield and grain baking quality parameters. Among the functional gene quantified, the archaeal amoA showed strong negative correlations with the wheat yields and many grain and flour quality parameters. Regression models were able to explain up to 81% of the variability in grain quality based on the microbial data from the May sampling. A better understanding of the microbiology of wheat fields could lead to an optimized management of the N fertilization to maximize yields and grain quality.

Arbuscular mycorrhiza has little influence on N2O potential emissions compared to plant diversity in experimental plant communities

Denitrification is an ecosystem process linked to ongoing climate change, because it releases nitrous oxide (N2O) into the atmosphere. To date, the literature covers mostly how aboveground (i.e. plant community structure) and belowground (i.e. plant-associated soil microbes) biota separately influence denitrification in isolation of each other. We here present a mesocosm experiment where we combine a manipulation of belowground biota (i.e. addition of Rhizophagus irregularis propagules to the indigenous mycorrhizal community) with a realized gradient in plant diversity. We used a seed mix containing plant species representative of mesophytic European grasslands and by stochastic differences in species establishment across the sixteen replicates per treatment level a spontaneously established gradient in plant diversity. We address mycorrhizal-induced and plant-diversity mediated changes on denitrification potential parameters and how these differ from the existing literature that studies them independently of each other. We show that unlike denitrification potential, N2O potential emissions do not change with mycorrhiza and depend instead on realized plant diversity. By linking mycorrhizal ecology to an N-cycling process, we present a comprehensive assessment of terrestrial denitrification dynamics when diverse plants co-occur.

Does Biological Denitrification Inhibition (BDI) in the Field Induce an Increase in Plant Growth and Nutrition in Apium graveolens L. Grown for a Long Period?

Intensive agriculture uses a lot of nitrogen fertilizers to increase crop productivity. These crops are in competition with soil-denitrifying microorganisms that assimilate nitrogen in the form of nitrate and transform it into N₂O, a greenhouse gas, or N₂. However, certain plant species exude secondary metabolites, called procyanidins, which inhibit denitrifiers and increase the nitrate pool in the soil available for plant nutrition. This phenomenon is called biological denitrification inhibition. Previously, we showed that the addition of exogenous procyanidins to a lettuce crop induces denitrifier inhibition and increases nitrate content in the soil, affecting lettuce morphological traits. Here, the effects of procyanidin amendments in the field on a more long-term and nitrogen-consuming crop species such as celery were tested. The effects of procyanidin amendment on celery growth with those of conventional ammonium nitrate amendments were, therefore, compared. Denitrification activity, nitrate concentration, the abundance of denitrifying bacteria in the soil, and traits related to celery growth were measured. It was shown that the addition of procyanidins inhibits denitrifiers and increases the soil nitrate level, inducing an improvement in celery morphological traits. In addition, procyanidin amendment induces the lowest nitrogen concentration in tissues and reduces N₂O emissions.

The N-fixing legume Periandra mediterranea constrains the invasion of an exotic grass (Melinis minutiflora P. Beauv) by altering soil N cycling

Melinis minutiflora is an invasive species that threatens the biodiversity of the endemic vegetation of the campo rupestre biome in Brazil, displacing the native vegetation and favouring fire spread. As M. minutiflora invasion has been associated with a high nitrogen (N) demand, we assessed changes in N cycle under four treatments: two treatments with contrasting invasion levels (above and below 50%) and two un-invaded control treatments with native vegetation, in the presence or absence of the leguminous species Periandra mediterranea. This latter species was considered to be the main N source in this site due to its ability to fix N2 in association with Bradyrhizobia species. Soil proteolytic activity was high in treatments with P. mediterranea and in those severely invaded, but not in the first steps of invasion. While ammonium was the N-chemical species dominant in plots with native species, including P.mediterranea, soil nitrate prevailed only in fully invaded plots due to the stimulation of the nitrifying bacterial (AOB) and archaeal (AOA) populations carrying the amoA gene. However, in the presence of P. mediterranea, either in the beginning of the invasion or in uninvaded plots, we observed an inhibition of the nitrifying microbial populations and nitrate formation, suggesting that this is a biotic resistance strategy elicited by P. mediterranea to compete with M. minutiflora. Therefore, the inhibition of proteolytic activity and the nitrification process were the strategies elicited by P.mediterranea to constrain M.munitiflora invasion.

Diversity analysis of the rhizospheric and endophytic bacterial communities of Senecio vulgaris L. (Asteraceae) in an invasive range

Increasing evidence has confirmed the importance of plant-associated bacteria for plant growth and productivity, and thus it is hypothesized that interactions between bacteria and alien plants might play an important role in plant invasions. However, the diversity of the bacterial communities associated with invasive plants is poorly understood. We therefore investigated the diversity of rhizospheric and endophytic bacteria associated with the invasive annual plant Senecio vulgaris L. (Asteraceae) based on 16S rRNA gene data obtained from 57 samples of four Senecio vulgaris populations in a subtropical mountainous area in central China. Significant differences in diversity were observed between plant compartments. Specifically, the rhizosphere harbored many more bacterial operational taxonomic units and showed higher alpha diversity than the leaf and root endospheres. The relative abundance profiles of the bacterial community composition differed substantially between the compartments and populations, especially at the phylum and family levels. However, the top five phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, and Acidobacteria) accounted for more than 90% of all the bacterial communities. Moreover, similar endophytic communities with a shared core set of bacteria were observed from different Senecio vulgaris populations. Heavy-metal-resistant, phosphate-solubilizing bacteria (Brevundimonas diminuta), nitrogen-fixing bacteria (Rhizobium leguminosarum), and cold-resistant bacteria (Exiguobacterium sibiricum) were present in the endosphere at relatively high abundance. This study, which reveals the structure of bacterial communities and their putative function in invasive Senecio vulgaris plants, is the first step in investigating the role of plant-bacteria interactions in the invasion of this species in China.

A case study of soil food web components affected by Fallopia japonica (Polygonaceae) in three natural habitats in Central Europe

This study determined the effect of the invasive plant Fallopia japonica on soil physical properties, microbial respiration, microbial biomass carbon content, enzymatic activities, and soil nematode communities. We established in total 30 plots in three natural habitats (forest, grassland, wetland) that were either uninvaded or mostly monospecifically invaded by F. japonica. The soil physical and microbial properties differed among the investigated plots, but the differences were observed to be non-significant between the invaded and the uninvaded plots. Non-metric multidimensional scaling based on nematode species diversity indicated that the total number of identified nematode species and their abundance were higher in the uninvaded compare to the invaded plots. Negative effect of F. japonica on omnivores, plant parasites, and root-fungal feeder nematodes was confirmed by their lower abundance in the invaded compared to the uninvaded plots. In the invaded plots, we also confirmed lower Maturity and Channel index, but higher Enrichment index. Our results thus indicated that the invasive plant F. japonica could affect nematode communities, more than physical or microbial properties, regardless of habitat.

This study determined the effect of the invasive plant Fallopia japonica on soil physical properties, microbial respiration, microbial biomass carbon content, enzymatic activities, and soil nematode communities. We established in total 30 plots in three natural habitats (forest, grassland, wetland) that were either uninvaded or mostly monospecifically invaded by F. japonica. The soil physical and microbial properties differed among the investigated plots, but the differences were observed to be non-significant between the invaded and the uninvaded plots. Non-metric multidimensional scaling based on nematode species diversity indicated that the total number of identified nematode species and their abundance were higher in the uninvaded compare to the invaded plots. Negative effect of F. japonica on omnivores, plant parasites, and root-fungal feeder nematodes was confirmed by their lower abundance in the invaded compared to the uninvaded plots. In the invaded plots, we also confirmed lower Maturity and Channel index, but higher Enrichment index. Our results thus indicated that the invasive plant F. japonica could affect nematode communities, more than physical or microbial properties, regardless of habitat.

Negative Effects of Copper Oxide Nanoparticles on Carbon and Nitrogen Cycle Microbial Activities in Contrasting Agricultural Soils and in Presence of Plants

Metal-oxide nanoparticles (NPs) such as copper oxide (CuO) NPs offer promising perspectives for the development of novel agro-chemical formulations of pesticides and fertilizers. However, their potential impact on agro-ecosystem functioning still remains to be investigated. Here, we assessed the impact of CuO-NPs (0.1, 1, and 100 mg/kg dry soil) on soil microbial activities involved in the carbon and nitrogen cycles in five contrasting agricultural soils in a microcosm experiment over 90 days. Additionally, in a pot experiment, we evaluated the influence of plant presence on the toxicity of CuO-NPs on soil microbial activities. CuO-NPs caused significant reductions of the three microbial activities measured (denitrification, nitrification, and soil respiration) at 100 mg/kg dry soil, but the low concentrations (0.1 and 1 mg/kg) had limited effects. We observed that denitrification was the most sensitive microbial activity to CuO-NPs in most soil types, while soil respiration and nitrification were mainly impacted in coarse soils with low organic matter content. Additionally, large decreases in heterotrophic microbial activities were observed in soils planted with wheat, even at 1 mg/kg for soil substrate-induced respiration, indicating that plant presence did not mitigate or compensate CuO-NP toxicity for microorganisms. These two experiments show that CuO-NPs can have detrimental effects on microbial activities in soils with contrasting physicochemical properties and previously exposed to various agricultural practices. Moreover, we observed that the negative effects of CuO-NPs increased over time, indicating that short-term studies (hours, days) may underestimate the risks posed by these contaminants in soils.

Within-species trade-offs in plant-stimulated soil enzyme activity and growth, flowering, and seed size

Soil microbial communities affect species demographic rates of plants. In turn, plants influence the composition and function of the soil microbiome, potentially resulting in beneficial feedbacks that alter their fitness and establishment. For example, differences in the ability to stimulate soil enzyme activity among plant lineages may affect plant growth and reproduction. We used a common garden study to test differences in plant-stimulated soil enzyme activity between lineages of the same species across developmental stages. Lineages employed different strategies whereby growth, days to flowering and seed size traded-off with plant-stimulated soil enzyme activity. Specifically, the smaller seeded lineage stimulated more enzyme activity at the early stage of development and flowered earlier while the larger seeded lineage sustained lower but consistent enzyme activity through development. We suggest that these lineages, which are both successful invaders, employ distinct strategies (a colonizer and a competitor) and differ in their influence on soil microbial activity. Synthesis. The ability to influence the soil microbial community by plants may be an important trait that trades off with growth, flowering, and seed size for promoting plant establishment, reproduction, and invasion.

Plant Nutrient Resource Use Strategies Shape Active Rhizosphere Microbiota Through Root Exudation

Plant strategies for soil nutrient uptake have the potential to strongly influence plant-microbiota interactions, due to the competition between plants and microorganisms for soil nutrient acquisition and/or conservation. In the present study, we investigate whether these plant strategies could influence rhizosphere microbial activities via root exudation, and contribute to the microbiota diversification of active bacterial communities colonizing the root-adhering soil (RAS) and inhabiting the root tissues. We applied a DNA-based stable isotope probing (DNA-SIP) approach to six grass species distributed along a gradient of plant nutrient resource strategies, from conservative species, characterized by low nitrogen (N) uptake, a long lifespans and low root exudation level, to exploitative species, characterized by high rates of photosynthesis, rapid rates of N uptake and high root exudation level. We analyzed their (i) associated microbiota composition involved in root exudate assimilation and soil organic matter (SOM) degradation by 16S-rRNA-based metabarcoding. (ii) We determine the impact of root exudation level on microbial activities (denitrification and respiration) by gas chromatography. Measurement of microbial activities revealed an increase in denitrification and respiration activities for microbial communities colonizing the RAS of exploitative species. This increase of microbial activities results probably from a higher exudation rate and more diverse metabolites by exploitative plant species. Furthermore, our results demonstrate that plant nutrient resource strategies have a role in shaping active microbiota. We present evidence demonstrating that plant nutrient use strategies shape active microbiota involved in root exudate assimilation and SOM degradation via root exudation.

Species composition, functional and phylogenetic distances correlate with success of invasive Chromolaena odorata in an experimental test

Biotic resistance may influence invasion success; however, the relative roles of species richness, functional or phylogenetic distance in predicting invasion success are not fully understood. We used biomass fraction of Chromolaena odorata, an invasive species in tropical and subtropical areas, as a measure of 'invasion success' in a series of artificial communities varying in species richness. Communities were constructed using species from Mexico (native range) or China (non-native range). We found strong evidence of biotic resistance: species richness and community biomass were negatively related with invasion success; invader biomass was greater in plant communities from China than from Mexico. Harvesting time had a greater effect on invasion success in plant communities from China than on those from Mexico. Functional and phylogenetic distances both correlated with invasion success and more functionally distant communities were more easily invaded. The effects of plant-soil fungi and plant allelochemical interactions on invasion success were species-specific.