Effects of precipitation change and nitrogen addition on the composition, diversity, and molecular ecological network of soil bacterial communities in a desert steppe

Additive Effects of Multiple Global Change Drivers on Terrestrial Nitrogen Cycling Worldwide

Global change has dramatically altered the Earth's biogeochemical cycles. However, the interactive effects of multiple global change factors (GCFs) on terrestrial nitrogen (N) cycling worldwide remain unclear, limiting the ability to predict how future global change will affect the global N cycle. We conducted a meta-analysis of 108 published articles to evaluate the main and interactive effects of elevated CO2, N addition, warming, and altered precipitation on soil N pools (NH4 +, NO3 -, and organic N) and transformation rates (N mineralization, nitrification, and denitrification) across terrestrial ecosystems. Results showed that single GCFs impacted the soil N cycle in different directions and magnitudes, with N addition and increased precipitation having the strongest positive effects on N pools and transformation rates, respectively. Moreover, the positive effects of N addition on the soil N cycle were generally enhanced when combined with other GCFs. Although the interactions of multiple GCFs were commonly additive (66.2%-83.3%), both synergistic (10.5%-15.1%) and antagonistic (2.8%-18.9%) effects were also observed. The types of treatment and ecosystem, geographic location, and climate all regulated the responses of soil N pools to GCFs to some degree, while only the types of treatment and ecosystem significantly affected the response of soil transformation rates to GCFs. These findings emphasize the importance of considering interactive effects among GCFs on terrestrial N cycling and highlight the necessity of incorporating these interactions into Earth system models for accurate predictions of N cycling responses to global changes.

Cascading impacts of nitrogen deposition on soil microbiome and herbivore communities in desert steppes

Human activities in the last century have intensified global nitrogen deposition, resulting in the degradation of ecosystem function and loss of biodiversity worldwide. Nitrogen addition is a crucial method for examining the effects of atmospheric nitrogen deposition on species composition and structure of soil microbiome and biotic community, as exogenous nitrogen inputs can trigger cascading effects on ecosystem functions. In a 6-year experiment, we evaluated the impact of nitrogen addition on soil microbial-plant-insect systems in desert steppes. Our results show that nitrogen addition significantly altered soil microbial composition and ecological function, leading to a decrease in nitrogen-fixing bacteria and an increase in saprophytic fungi. High levels of nitrogen addition increased total plant biomass while decreasing species diversity. Additionally, high nitrogen addition levels suppressed below-ground biomass of gramineae and legumes compared to low nitrogen addition. Nitrogen addition also increased herbivore abundance by altering insect community structure, particularly benefiting chewing pests over sucking pests, thus heightening the risk of biological disasters through trophic cascading effects. Consequently, excessive nitrogen addition may destabilize desert steppe ecosystems by disturbing soil microbial-plant-insect interactions, hindering the maintenance of biotic community diversity and steppe productivity.

Long-term grazing reduces soil fungal network complexity but enhances plant-soil microbe network connectivity in a semi-arid grassland

Grazing plays a significant role in shaping both aboveground vegetation and belowground microbial communities in arid and semi-arid grasslands, which in turn affects ecosystem functions and sustainability. Therefore, it was essential to implement effective grazing management practices to preserve ecological balance and support sustainable development in these delicate environments. To optimize the traditional continuous grazing policy, we conducted a 10-year seasonal grazing experiment with five treatments in a typical grassland in northern China: no grazing (NG), continuous summer grazing (CG), and three seasonal grazing treatments (G57 in May and July, G68 in June and August, and G79 in July and September). Our study found that although grazing reduced plant community biomass, G68 treatment maintained high plant height and community diversity (P < 0.05). Grazing did not affect soil bacterial and archaeal alpha diversity, but CG treatment reduced soil fungal diversity (P < 0.05). CG reduced the archaeal network's vertices (which represent microbial taxa, OTUs) and connections (ecological interactions between taxa), but seasonal grazing increased its complexity. Furthermore, grazing did not change bacterial networks but enhanced cross-domain interactions (relationships between different biological groups) of plant-soil fungi and plant-soil archaea. Overall, we used the Mantel test to find that soil microbial diversity was positively correlated with soil physicochemical properties rather than plant community characteristics after grazing. These findings are beneficial for the optimization of sustainable grassland management policies and the protection of plant and soil biodiversity.

Land use modified impacts of global change factors on soil microbial structure and function: A global hierarchical meta-analysis

Nitrogen cycling in terrestrial ecosystems is critical for biodiversity, vegetation productivity and biogeochemical cycling. However, little is known about the response of functional nitrogen cycle genes to global change factors in soils under different land uses. Here, we conducted a multiple hierarchical mixed effects meta-analyses of global change factors (GCFs) including warming (W+), mean altered precipitation (MAP+/-), elevated carbon dioxide concentrations (eCO2), and nitrogen addition (N+), using 2706 observations extracted from 200 peer-reviewed publications. The results showed that GCFs had significant and different effects on soil microbial communities under different types of land use. Under different land use types, such as Wetland, Tundra, Grassland, Forest, Desert and Agriculture, the richness and diversity of soil microbial communities will change accordingly due to differences in vegetation cover, soil management practices and environmental conditions. Notably, soil bacterial diversity is positively correlated with richness, but soil fungal diversity is negatively correlated with richness, when differences are driven by GCFs. For functional genes involved in nitrification, eCO2 in agricultural soils and the interaction of N+ with other GCFs in grassland soils stimulate an increase in the abundance of the AOA-amoA gene. In agricultural soil, MAP+ increases the abundance of nifH. W+ in agricultural soils and N+ in grassland soils decreased the abundance of nifH. The abundance of the genes nirS and nirK, involved in denitrification, was mainly negatively affected by W+ and positively affected by eCO2 in agricultural soil, but negatively affected by N+ in grassland soil. This meta-analysis was important for subsequent research related to global climate change. Considering data limitations, it is recommended to conduct multiple long-term integrated observational experiments to establish a scientific basis for addressing global changes in this context.

Tree age affects carbon sequestration potential via altering soil bacterial community composition and function

Among various factors related to the forest carbon pool, the tree stand age, which interacts with soil organic matter, decomposition rates, and microbial activity, is essential and cannot be disregarded. However, knowledge about how tree phases influence soil carbon sinks is not adequate. This study sampled Larix kaempferi (Japanese larch) plantations with different tree stand ages to investigate the temporal dynamics of soil carbon sink in the forest. Physiochemical analyses and high-throughput sequencing results further revealed the interactions of tree stands and their related rhizosphere microbiome. It was found that microbial composition and metabolic activity were significantly affected by different tree ages, whose structures gradually diversified and became more stable from young to mature forests. Many keystone taxa from the phyla Chloroflexi, Proteobacteria, Acidobacteriota, and Nitrospirota were found to be associated with carbon transformation processes. Interestingly, the carbon resource utilization strategies of microbial groups related to tree ages also differed, with near-mature forest soils showing better labile carbon degradation capacity, and mature forests possessing higher degradation potential of recalcitrant carbon. Age-altered tree growth and physiology were found to interact with its rhizosphere microbiome, which is the driving factor in the formation and stability of forest soil carbon. This study highlighted that the tree age-associated soil microbiomes, which provided insights into their effects on soil carbon transformation, were significant in enhancing the knowledge of carbon sequestration in L. kaempferi plantations.

Response of microbial communities to the changes in grazing intensity and season in a typical steppe

Livestock grazing is an influencing factor playing a key role in shaping the plant community, microbial community, and soil properties in grassland ecosystems. Northern China's Loess Plateau has been used for livestock grazing for centuries and is a vulnerable ecosystem. In this study, the fates of bacterial and fungal communities of the typical steppe of the Loess Plateau were investigated under increasing grazing intensities practiced in summer and winter seasons. The results revealed changes in soil physiochemical properties, plant community properties, and microbial diversity in response to alterations in the grazing intensity. The alpha diversity of microbial communities (including bacteria and fungi) exhibited an uneven trend during summer grazing due to an increase in grazing intensity, but it decreased during winter grazing; however, the observed changes were not significant. The beta diversity of the bacterial community was highly influenced by grazing intensity, the summer community clustered near nongrazing, and the winter community presented significantly different results. The beta diversity of the fungal community was not influenced by grazing intensity or season. Grazing induced the growth of fast-growing bacteria (such as Actinobacteria and Firmicutes) and saprophytic fungi and a reduction in overall pathogenic traits. Co-occurrence network analysis and a structural equation model revealed changes in soil and plant properties (such as soil nitrogen level, soil organic carbon level, aboveground biomass, and litter biomass), with an increase in grazing intensity contributing to alterations in bacterial and fungal diversities. This finding demonstrates that grazing intensity can directly affect soil microbes and play an indirect role by modifying soil nutrients and reducing plant biomass, which eventually contributes to changes in microbial communities. Overall, implementing low grazing intensity is suggested for maintaining the microbial community structure the same as that of the native microbiome (ungrazed) in the steppe ecosystems.

Identification of bacteria and fungi responsible for litter decomposition in desert steppes via combined DNA stable isotope probing

Introduction

Soil microorganisms play crucial roles in determining the fate of litter in desert steppes because their activities constitute a major component of the global carbon (C) cycle. Human activities lead to increased ecosystem nitrogen (N) deposition, which has unpredictable impacts on soil microorganism diversity and functions. Nowadays, it is necessary to further study the succession of these microorganisms in the process of litter decomposition in desert steppe, and explore the effect of N deposition on this process. This issue is particularly important to resolve because it contributes to the broader understanding of nutrient cycling processes in desert steppes.

Methods

In this study, DNA stable isotope probing (DNA-SIP) was used to study changes in soil bacterial and fungal community composition and function during 8 weeks of culture of 13C-labeled litter in desert steppes.

Results

The results were as follows: (1) Actinomycetota, Pseudomonadota, and Ascomycota are the main microorganisms involved in litter decomposition in desert steppes; (2) N deposition (50 kg ha-1 year-1) significantly increased the relative abundance of some microorganisms involved in the decomposition process; and (3) N deposition likely promotes litter decomposition in desert steppes by increasing the abundances of N cycles bacteria (usually carrying GH family functional genes).

Discussion

These findings contribute to a deeper understanding of the C assimilation mechanisms associated with litter residue production, emphasizing the importance of extensive C utilization.

Land use conversion increases network complexity and stability of soil microbial communities in a temperate grassland

Soils harbor highly diverse microbial communities that are critical to soil health, but agriculture has caused extensive land use conversion resulting in negative effects on critical ecosystem processes. However, the responses and adaptations of microbial communities to land use conversion have not yet been understood. Here, we examined the effects of land conversion for long-term crop use on the network complexity and stability of soil microbial communities over 19 months. Despite reduced microbial biodiversity in comparison with native tallgrass prairie, conventionally tilled (CT) cropland significantly increased network complexity such as connectivity, connectance, average clustering coefficient, relative modularity, and the number of species acting at network hubs and connectors as well as resulted in greater temporal variation of complexity indices. Molecular ecological networks under CT cropland became significantly more robust and less vulnerable, overall increasing network stability. The relationship between network complexity and stability was also substantially strengthened due to land use conversion. Lastly, CT cropland decreased the number of relationships between network structure and environmental properties instead being strongly correlated to management disturbances. These results indicate that agricultural disturbance generally increases the complexity and stability of species "interactions", possibly as a trade-off for biodiversity loss to support ecosystem function when faced with frequent agricultural disturbance.

Vertical and seasonal dynamics of bacterial pathogenic communities at an aged organic contaminated site: Insights into microbial diversity, composition, interactions, and assembly processes

Under the background of the Coronavirus Disease 2019 (COVID-19) pandemic, research on pathogens deserves greater attention in the natural environment, especially in the widely distributed contaminated sites with complicated and severe organic pollution. In this study, the community composition and assembly of soil pathogens identified by the newly-developed 16S-based pipeline of multiple bacterial pathogen detection (MBPD) have been investigated on spatiotemporal scales in the selected organic polluted site. We demonstrated that the richness and diversity of the pathogenic communities were primarily controlled by soil depth, while the structure and composition of pathogenic communities varied pronouncedly with seasonal changes, which were driven by the alterations in both physiochemical parameters and organic contaminants over time. Network analysis revealed that the overwhelmingly positive interactions, identified multiple keystone species, and a well-organized modular structure maintained the stability and functionality of the pathogenic communities under environmental pressures. Additionally, the null-model analysis showed that deterministic processes dominated the pathogenic community assembly across soil profiles. In three seasons, stochasticity-dominated processes in spring and summer changed into determinism-dominated processes in winter. These findings extend our knowledge of the response of the bacterial pathogenic community to environmental disruptions brought on by organic contaminated sites.

Glacial Influence Affects Modularity in Bacterial Community Structure in Three Deep Andean North-Patagonian Lakes

We analyze the bacteria community composition and the ecological processes structuring these communities in three deep lakes that receive meltwater from the glaciers of Mount Tronador (North-Patagonia, Argentina). Lakes differ in their glacial connectivity and in their turbidity due to glacial particles. Lake Ventisquero Negro is a recently formed proglacial lake and it is still in contact with the glacier. Lakes Mascardi and Frías lost their glacial connectivity during the Pleistocene-Holocene transition. Total dissolved solid concentration has a significant contribution to the environmental gradient determining the segregation of the three lakes. The newly formed lake Ventisquero Negro conformed a particular bacterial community that seemed to be more related to the microorganisms coming from glacier melting than to the other lakes of the basin. The net relatedness index (NRI) showed that the bacterial community of lake Ventisquero Negro is determined by environmental filtering, while in the other lakes, species interaction would be a more important driver. The co-occurrence network analysis showed an increase in modularity and in the number of modules when comparing Lake Ventisquero Negro with the two large glacier-fed lakes suggesting an increase in heterogeneity. At the same time, the presence of modules with phototrophic bacteria (Cyanobium strains) in lakes Frías and Mascardi would reflect the increase of this functional photosynthetic association. Overall, our results showed that the reduction in ice masses in Patagonia will affect downstream large deep Piedmont lakes losing the glacial influence in their bacterial communities.

High Ammonium Addition Changes the Diversity and Structure of Bacterial Communities in Temperate Wetland Soils of Northeastern China

The soil microbiome is an important component of wetland ecosystems and plays a pivotal role in nutrient cycling and climate regulation. Nitrogen (N) addition influences the soil's microbial diversity, composition, and function by affecting the soil's nutrient status. The change in soil bacterial diversity and composition in temperate wetland ecosystems in response to high ammonium nitrogen additions remains unclear. In this study, we used high-throughput sequencing technology to study the changes of soil bacterial diversity and community structure with increasing ammonium concentrations [CK (control, 0 kg ha-1 a-1), LN (low nitrogen addition, 40 kg ha-1 a-1), and HN (high nitrogen addition, 80 kg ha-1 a-1)] at a field experimental site in the Sanjiang Plain wetland, China. Our results showed that except for soil organic carbon (SOC), other soil physicochemical parameters, i.e., soil moisture content (SMC), dissolved organic nitrogen (DON), total nitrogen (TN), pH, ammonium nitrogen (NH4+), and dissolved organic carbon (DOC), changed significantly among three ammonium nitrogen addition concentrations (p < 0.05). Compared to CK, LN did not change soil bacterial α-diversity (p > 0.05), and HN only decreased the Shannon (p < 0.05) and did not change the Chao (p > 0.05) indices of soil bacterial community. Ammonium nitrogen addition did not significantly affect the soil's bacterial community structure based on non-metric multidimensional scaling (NMDS) and PERMANOVA (ADONIS) analyses. Acidobacteriota (24.96-31.11%), Proteobacteria (16.82-26.78%), Chloroflexi (10.34-18.09%), Verrucomicrobiota (5.23-11.56%), and Actinobacteriota (5.63-8.75%) were the most abundant bacterial phyla in the soils. Nitrogen addition changed the complexity and stability of the bacterial network. SMC, NO3-, and pH were the main drivers of the bacterial community structure. These findings indicate that enhanced atmospheric nitrogen addition may have an impact on bacterial communities in soil, and this study will allow us to better understand the response of the soil microbiome in wetland ecosystems in the framework of increasing nitrogen deposition.

Immediate response of paddy soil microbial community and structure to moisture changes and nitrogen fertilizer application

Water and fertilizer managements are the most common practices to maximize crop yields, and their long-term impact on soil microbial communities has been extensively studied. However, the initial response of microbes to fertilization and soil moisture changes remains unclear. In this study, the immediate effects of nitrogen (N)-fertilizer application and moisture levels on microbial community of paddy soils were investigated through controlled incubation experiments. Amplicon sequencing results revealed that moisture had a stronger influence on the abundance and community composition of total soil bacteria, as well as ammonia oxidizing-archaea (AOA) and -bacteria (AOB). Conversely, fertilizer application noticeably reduced the connectivity and complexity of the total bacteria network, and increasing moisture slightly exacerbated these effects. NH4+-N content emerged as a significant driving force for changes in the structure of the total bacteria and AOB communities, while NO3--N content played more important role in driving shifts in AOA composition. These findings indicate that the initial responses of microbial communities, including abundance and composition, and network differ under water and fertilizer managements. By providing a snapshot of microbial community structure following short-term N-fertilizer and water treatments, this study contributes to a better understanding of how soil microbes respond to long-term agriculture managements.

Distinct Responses of Abundant and Rare Soil Bacteria to Nitrogen Addition in Tropical Forest Soils

Soil microbial responses to anthropogenic nitrogen (N) enrichment at the overall community level has been extensively studied. However, the responses of community dynamics and assembly processes of the abundant versus rare bacterial taxa to N enrichment have rarely been assessed. Here, we present a study in which the effects of short- (2 years) and long-term (13 years) N additions to two nearby tropical forest sites on abundant and rare soil bacterial community composition and assembly were documented. The N addition, particularly in the long-term experiment, significantly decreased the bacterial α-diversity and shifted the community composition toward copiotrophic and N-sensitive species. The α-diversity and community composition of the rare taxa were more affected, and they were more closely clustered phylogenetically under N addition compared to the abundant taxa, suggesting the community assembly of the rare taxa was more governed by deterministic processes (e.g., environmental filtering). In contrast, the abundant taxa exhibited higher community abundance, broader environmental thresholds, and stronger phylogenetic signals under environmental changes than the rare taxa. Overall, these findings illustrate that the abundant and rare bacterial taxa respond distinctly to N addition in tropical forests, with higher sensitivity of the rare taxa, but potentially broader environmental acclimation of the abundant taxa. IMPORTANCE Atmospheric nitrogen (N) deposition is a worldwide environmental problem and threatens biodiversity and ecosystem functioning. Understanding the responses of community dynamics and assembly processes of abundant and rare soil bacterial taxa to anthropogenic N enrichment is vital for the management of N-polluted forest soils. Our sequence-based data revealed distinct responses in bacterial diversity, community composition, environmental acclimation, and assembly processes between abundant and rare taxa under N-addition soils in tropical forests. These findings provide new insight into the formation and maintenance of bacterial diversity and offer a way to better predict bacterial responses to the ongoing atmospheric N deposition in tropical forests.

The addition of biochar and nitrogen alters the microbial community and their cooccurrence network by affecting soil properties

Biochar plays an important role in reducing the harmful environmental effects of inorganic nitrogen (N) fertilizers on agroecosystems, but the the impact mechanisms of biochar combined with N fertilizers on soil microorganisms are not clear enough. In this study, high-throughput sequencing was used to study the influences of three N fertilizer levels (0 (N0), 90 (N90) and 120 (N120) kg ha^-1) and two biochar levels (0 (B0) and 20 (B20) t ha^-1) on the soil microbial community and symbiotic network among microbial taxa in wheat fields. Compared to the control (B0N0), N fertilizer alone or combined with biochar significantly increased soil total N, available N, and organic matter in topsoil (0-20 cm), and the same results were found only in B20N120 treatment in subsoil (20-40 cm). In addition, bacterial and fungal diversity in topsoil were significantly increased and decreased by all N and biochar treatments, respectively. Moreover, soil bacterial and fungal community compositions also were also changed by N and biochar. Furthermore, biochar weakened the competition and cooperation among microorganisms in topsoil and subsoil, and the keystone species of networks were also changed by biochar. Redundancy analysis showed that soil total N, available N, available P, available K and pH were the main environmental factors driving the changes in bacterial and fungal community structures. These data indicated that the addition of N fertilizer and biochar could improve soil fertility by maintaining the stability of microbial community structures, which can provide reasonable guidance for the sustainable development of agriculture, such as maintaining dryland production.

Impact of Drip Irrigation and Nitrogen Fertilization on Soil Microbial Diversity of Spring Maize

Given the shortage of water resources and excessive application of nitrogen fertilizers in irrigated areas, we explored the effect of water−nitrogen coupling on soil microbial diversity in maize fields irrigated using shallow buried droppers. A field experiment (split-plot design) was used with irrigation amounts set at 40%, 50%, and 60% of the conventional amount; furthermore, 13 water and nitrogen coupling treatments were designed. The secondary area was the nitrogen application level, corresponding to 50%, 70%, and the original conventional application amounts. The results showed that the effect of irrigation amount on bacterial community composition was greater than that of nitrogen, whereas the effect of nitrogen on fungi was greater than that on bacteria. No significant difference was detected in the α diversity index or species richness of bacteria and fungi. Available phosphorus and organic carbon contents significantly correlated with the community structure of soil bacteria (p < 0.05). The relative abundances of bacteria and fungi were stable with the decrease of nitrogen application rate at the irrigation rate of 2000 m3 ha−1. With the decrease of irrigation amount, the relative abundance of bacteria and fungi was stable under the treatment of 210 kg ha−1 nitrogen fertilizer. Moreover, the relative abundance of nitrogen-fixing bacteria related to the nitrogen cycle was increased by irrigation of 2000 m3 ha−1 and nitrogen application of 210 kg ha−1. Moderate reduction of subsequent N supply should be as a prior soil management option in a high N input agroecosystem.

Responses of soil bacterial communities to precipitation change in the semi-arid alpine grassland of Northern Tibet

A change in precipitation can profoundly change the structure of soil microbial communities, especially in arid and semi-arid areas which are limited by moisture conditions. Therefore, it is crucial to explore how soil bacterial community composition and diversity will respond to variation in precipitation. Here we conducted a precipitation control experiment to simulate precipitation change by reducing and increasing rainfall by 25%, 50%, and 75% in the alpine grasslands of northern Tibet. The composition, diversity, and species interaction network of soil microbial community were studied by high-throughput sequencing, and the relationship between microbial community species and soil environmental factors was analyzed. Our results showed that Proteobacteria (45%-52%) and Actinobacteria (37%-45%) were the dominant bacteria in the soil. The alpha diversity index based on Shannon, Chao1, and Simpson indices revealed that precipitation change had no significant effect on richness and evenness of soil microbial communities. Non-metric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM) showed that a clear separation of soil microbial communities between D2(-50%),D3(-75%) and W2(+50%), W3(+75%) treatments. The microbial interaction network indicated that the water-increasing treatment group had closer connections, and Proteobacteria and Actinomycetes were the core species. Furthermore, there was a stronger positive correlation between species in the water-reducing treatment group, the contribution of Proteobacteria decreased significantly, the role of connecting hub decreased, and Actinomycetes became the most important core microbial species. In addition, soil water content (SWC) and available phosphorus (AP) were closely related to the variations in soil microbial compositions. The findings of this study provide a theoretical basis for the driving mechanism of global climate change on soil microbial community and grassland ecosystem in alpine grassland.

Construction Means of Soil Microbial Synusiologic Network Based on ANN

With the construction of synusiologic civilization and synusiologic environmental protection entering a new era driven by data, the breadth and depth of application of the DM technique in the domain of synusiologic environmental protection are constantly strengthened. If reasonable planning is not carried out in the process of social construction, it will cause unpredictable damage to the synusiologic environment. However, traditional synusiologic planning means too much human interference, and there are still some shortcomings in accuracy and operability, which means they cannot guide synusiologic construction well. In order to analyze the contribution of the soil nutrient data to soil fertility and dig out the knowledge describing soil fertility, this paper studies the construction means of soil microbial synusiologic network by ANN. By simulating the learning, memorizing, and processing problems of human brain neurons, the artificial network establishes a parallel distributed processing system computing DMG model with a large number of connections, which can quickly acquire knowledge from the outside world and store and process it and respond to the changes in the external environment in time. According to the research in this paper, the network performance of this algorithm is 18% better than that of the traditional algorithm, and it is suitable to be widely put into practice.

Nitrogen use aggravates bacterial diversity and network complexity responses to temperature

Rising temperature affects microbial composition and function in agriculture field, especially under nitrogen fertilization. In this study, we investigated the bacterial community of paddy soil incubated at controlled temperatures (5 °C, 15 °C, 25 °C, and 35 °C). Results showed that the response of bacterial communities to temperature was not uniform. Temperature elevation from 15 to 25 °C abruptly shifted the soil bacterial community, whereas elevation from 5 to 15 °C and from 25 to 35 °C had a marginal effect. The bacterial α-diversity was higher at 5 °C and 15 °C, owing to the massively distributed taxa with low abundance. However, as the temperature increased to 25 °C and 35 °C, these taxa were diminished, whereas Firmicutes significantly increased, resulting in a strong decline in α-diversity. Simultaneously, bacterial network complexity significantly increased at 25 °C and 35 °C, indicating the bacteria had closer interactions. Nitrogen application aggravated the variation in bacterial diversity and network complexity among temperatures. Interestingly, most complex network was observed under higher temperatures in fertilized soils. Collectively, these results indicate that nitrogen exacerbates the response of the soil bacterial community to temperature, and association between diversity and network complexity may be present.

Fungal Communities Are More Sensitive to the Simulated Environmental Changes than Bacterial Communities in a Subtropical Forest: the Single and Interactive Effects of Nitrogen Addition and Precipitation Seasonality Change

Increased nitrogen deposition (N factor) and changes in precipitation patterns (W factor) can greatly impact soil microbial communities in tropical/subtropical forests. Although knowledge about the effects of a single factor on soil microbial communities is growing rapidly, little is understood about the interactive effects of these two environmental change factors. In this study, we investigated the responses of soil bacterial and fungal communities to the short-term simulated environmental changes (nitrogen addition, precipitation seasonality change, and their combination) in a subtropical forest in South China. The interaction between N and W factors was detected significant for affecting some soil physicochemical properties (such as pH, soil water, and NO₃^- contents). Fungi were more susceptible to treatment than bacteria in a variety of community traits (alpha, beta diversity, and network topological features). The N and W factors act antagonistically to affect fungal alpha diversity, and the interaction effect was detected significant for the dry season. The topological features of the meta-community (containing both bacteria and fungi) network overrode the alpha and beta diversity of bacterial or fungal communities in explaining the variation of soil enzyme activities. The associations between Ascomycota fungi and Gammaproteobacteria or Alphaproteobacteria might be important in mediating the inter-kingdom interactions. In summary, our results suggested that fungal communities were more sensitive to N and W factors (and their interaction) than bacterial communities, and the treatments' effects were more prominent in the dry season, which may have great consequences in soil processes and ecosystem functions in subtropical forests.

Different Responses of Soil Bacterial Communities to Nitrogen Addition in Moss Crust

Bacterial communities in soil serve an important role in controlling terrestrial biogeochemical cycles and ecosystem processes. Increased nitrogen (N) deposition in Northwest China is generating quantifiable changes in many elements of the desert environment, but the impacts of N deposition, as well as seasonal variations, on soil bacterial community composition and structure are poorly understood. We used high-throughput sequencing of bacterial 16S rRNA genes from Gurbantünggüt Desert moss crust soils to study the impacts of N addition on soil bacterial communities in March, May, and November. In November, we discovered that the OTU richness and diversity of soil bacterial community dropped linearly with increasing N input. In November and March, the diversity of the soil bacterial community decreased significantly in the medium-N and high-N treatments. In May, N addition caused a substantial change in the makeup of the soil bacterial composition, while the impacts were far less apparent in November and March. Furthermore, the relative abundance of major bacterial phyla reacted non-linearly to N addition, with high-N additions decreasing the relative richness of Proteobacteria, Bacteroidetes, and Acidobacteria while increasing the relative abundance of Actinobacteria and Chloroflexi. We also discovered that seasonality, as characterized by changes in soil moisture, pH, SOC, and AK content, had a significant impact on soil bacterial communities. Significant variations in the makeup of the community were discovered at the phylum and genus levels throughout the various months. In May, the variety of soil bacterial community was at its peak. Further investigation showed that the decrease in soil bacterial diversity was mostly attributed to a drop in soil pH. These results indicated that the impact of N deposition on the soil bacterial community was seasonally dependent, suggesting that future research should evaluate more than one sample season at the same time.