Responses of Soil Bacterial Communities to Nitrogen Deposition and Precipitation Increment Are Closely Linked with Aboveground Community Variation

Metagenomic analysis reveal the phytoremediation effects of monocropping and intercropping of halophytes Halogeton glomeratus and Suaeda glauca in saline soil of Northwestern China

AIMS

Planting halophytes is a widely used method of phytoremediation for saline soils. The succulent halophytes Halogeton glomeratus and Suaeda glauca are widely used for remediation of saline soil in the arid region of Northwestern China. However, whether intercropping of H. glomeratus and S. glauca can increase the improvement effect for saline soil is yet to be proved.

MATERIALS AND METHODS

Therefore, this study analyzed three phytoremediation planting modes: monocropping of H. glomeratus (Hg), monocropping of S. glauca (Sg), and H. glomeratus and S. glauca intercropping (Hg||Sg). These were applied in field experiments, with biomass and soil physicochemical properties measured for each treatment, and the mechanism was analyzed using macrogenomics.

RESULTS

After harvesting the halophytes after one season, the Hg treatment had the highest dry biomass and soil total dissolved salt content was reduced; correspondingly, soil pH were decreased and soil organic matter content were increased. The results showed that Actinobacteria, Acidobacteria and Proteobacteria were the dominant phylum under the four treatments. This suggests that Hg treatment was more capable of producing microorganisms favorable to saline soil remediation.

CONCLUSIONS

Thus, H. glomeratus monocropping is a more effective phytoremediation strategy for saline soil in the dry zone of Northwestern China.

Nitrogen addition restricts key soil ecological enzymes and nutrients by reducing microbial abundance and diversity

Microorganisms are critical in forest ecosystems, where they secrete soil ecological enzymes and mediate nutrient cycling. These processes are essential in determining how these ecosystems respond to nitrogen (N) addition inputs. In this study, an N addition experiment was conducted with three levels of N addition treatments in a subtropical evergreen broad-leaved forest in southwest China. The aim was to identify the effects of low (LN: 10 g m- 2 year-1), medium (MN: 20 g m- 2 year- 1), and high N addition (HN: 25 g m- 2 year- 1) on soil microbial community structure, diversity, ecological enzyme activities, and nutrient content, and to explore whether and how soil microorganisms influence ecological enzyme activity and nutrient cycling. Our observations indicated that surface soil exhibited the highest microbial diversity, ecological enzyme activities, and nutrient contents. N addition led to a reduction in soil bacterial and fungal diversity, with bacterial diversity consistently higher than fungal diversity. Moreover, bacterial community structures were generally more diverse and complex compared to fungal communities. The study emphasized that bacteria were relatively enriched under LN treatment, while fungi exhibited higher relative abundance under control conditions. Different soil microbial groups exhibited distinct responses to N addition, with an inhibitory effect on enzyme activities such as invertase (Inv), urease (Ure), and acid phosphatase (ACP), and an enhancement of catalase (CAT) activity. With increasing N addition levels, soil organic carbon (SOC), total N (TN), and total phosphorus (TP) contents decreased, whereas total potassium (TK), nitrate N (NO3--N), and ammonium N (NH4+-N) exhibited the opposite trend. Co-linearity network analysis revealed stronger interactions among soil bacteria compared to fungi. The dominant bacterial phyla Pseudomonadota and Verrucomicrobiota showed stronger correlations with Ure and ACP, respectively, while Acidobacteriota exhibited a higher correlation with TP. Among the dominant fungal phyla, Basidiomycota had stronger correlations with CAT, NO3--N, and NH4+-N, while Ascomycota was notably associated with Inv. The results showed that soil bacteria had a strong correlation with ecological enzymes, while soil fungi had a strong correlation with nutrients. This implies that bacteria and fungi have distinct advantages in enzyme secretion and nutrient mediation, leading to a trend of nutritional complementarity.

Effects of Biological Nitrogen Fixation and Nitrogen Deposition on Soil Microbial Communities in Karst Grassland Ecosystems

Diverse exogenous nitrogen (N) sources have a considerable impact on microbial community structure in terrestrial ecosystems. Legume plants and N deposition can relieve N limitations and increase net primary productivity. However, the differences in their effects on soil microbial communities remain unclear. Here, the responses of the soil microbial community to a legume-planting system and simulated N deposition were examined in karst grasslands in Southwest China over five years by analyzing soil microbial phospholipid fatty acids (PLFAs). The experiment included three treatments-legume plant introduction (NL, Indigofera atropurpurea), N deposition (ND, NH4NO3:10 g N m-2 yr-1), and a control with no treatment. The effects of NL and ND on soil microbial community composition differed significantly. ND significantly reduced the biomass of bacteria, actinobacteria, and arbuscular mycorrhizal fungi. NL insignificantly increased the biomass of all microbial groups. However, the total amounts of PLFAs and fungal biomass were significantly higher in NL than in ND. The effect of legume plant introduction on soil microbial community composition was more powerful than that of ND. Overall, the introduction of legume plants is beneficial in terms of increasing the biomass of the soil microbial community and stabilizing the soil microbial community structure in karst grassland ecosystems.

Exploring the Rhizospheric Microbial Communities under Long-Term Precipitation Regime in Norway Spruce Seed Orchard

The rhizosphere is the hotspot for microbial enzyme activities and contributes to carbon cycling. Precipitation is an important component of global climate change that can profoundly alter belowground microbial communities. However, the impact of precipitation on conifer rhizospheric microbial populations has not been investigated in detail. In the present study, using high-throughput amplicon sequencing, we investigated the impact of precipitation on the rhizospheric soil microbial communities in two Norway Spruce clonal seed orchards, Lipová Lhota (L-site) and Prenet (P-site). P-site has received nearly double the precipitation than L-site for the last three decades. P-site documented higher soil water content with a significantly higher abundance of Aluminium (Al), Iron (Fe), Phosphorous (P), and Sulphur (S) than L-site. Rhizospheric soil metabolite profiling revealed an increased abundance of acids, carbohydrates, fatty acids, and alcohols in P-site. There was variance in the relative abundance of distinct microbiomes between the sites. A higher abundance of Proteobacteria, Acidobacteriota, Ascomycota, and Mortiellomycota was observed in P-site receiving high precipitation, while Bacteroidota, Actinobacteria, Chloroflexi, Firmicutes, Gemmatimonadota, and Basidiomycota were prevalent in L-site. The higher clustering coefficient of the microbial network in P-site suggested that the microbial community structure is highly interconnected and tends to cluster closely. The current study unveils the impact of precipitation variations on the spruce rhizospheric microbial association and opens new avenues for understanding the impact of global change on conifer rizospheric microbial associations.

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.

The Heterogeneous Habitat of Taiga Forests Changes the Soil Microbial Functional Diversity

The soil contains abundant and diverse microorganisms, which interrelate closely with the aboveground vegetation and impact the structure and function of the forest ecosystem. To explore the effect of vegetation diversity on soil microbial functional diversity in taiga forests, we selected significantly different important values of Larix gmelinii as experimental grouping treatments based on plant investigation from fixed plots in Da Xing'anling Mountains. Following that, we collected soil samples and applied the Biolog-ECO microplate method to investigate differences in carbon source utilization, features of functional diversity in soil microorganisms, and factors influencing them in taiga forests. The AWCD decreased as the important value of Larix gmelinii grew, and soil microorganisms preferred carboxylic acids, amino acids, and carbohydrates over polymers, phenolic acids, and amines. The Shannon and McIntosh indexes decreased significantly with the increase of the important value of Larix gmelinii (p < 0.05) and were positively correlated with soil SOC, MBC, C/N, and pH, but negatively with TN, AP, and AN. Redundancy analysis revealed significant effects on soil microbial functional diversity from soil C/N, SOC, AP, MBC, TN, pH, AN, and WC. To sum up, heterogeneous habitats of taiga forests with different important values altered soil microbial functional diversity.

The impact of smash-ridge tillage on agronomic traits of tobacco plants, soil enzymatic activity, microbial community structure, and functional diversity

Smash-ridge tillage is a novel cultivation technique that significantly influences the quality of arable land and crop yield. In this study, we employed high-throughput 16S rRNA sequencing and Biolog-ECO methods to systematically investigate the impact of smash-ridge tillage on soil microbial community structure and functional diversity. The results demonstrate that both ST30 and ST50 treatments significantly enhance the average plant height, average plant diameter, average fresh root weight, stem fresh weight, and leaf area of tobacco plants, with the ST50 treatment exhibiting superior performance. Furthermore, both ST30 and ST50 treatments exhibit significantly higher soil enzyme activity and microbial community diversity compared to the CK treatment. They also improve the soil microbial utilization of carbon sources. Additionally, the ST50-treated soil samples demonstrate 15 microbial functional pathways that exceed those of the CK and ST30 treatments. In conclusion, the Smash-ridge tillage treatment at a depth of 50 cm yields more favorable results. This study provides a theoretical foundation for enhancing soil quality in Smash-ridge tillage by elucidating the mechanisms through which it impacts soil microbial ecology.

C:N:P stoichiometry of plants, soils, and microorganisms: Response to altered precipitation

Precipitation changes modify C, N, and P cycles, which regulate the functions and structure of terrestrial ecosystems. Although altered precipitation affects above- and belowground C:N:P stoichiometry, considerable uncertainties remain regarding plant-microbial nutrient allocation strategies under increased (IPPT) and decreased (DPPT) precipitation. We meta-analyzed 827 observations from 235 field studies to investigate the effects of IPPT and DPPT on the C:N:P stoichiometry of plants, soils, and microorganisms. DPPT reduced leaf C:N ratio, but increased the leaf and root N:P ratios reflecting stronger decrease of P compared with N mobility in soil under drought. IPPT increased microbial biomass C (+13%), N (+15%), P (26%), and the C:N ratio, whereas DPPT decreased microbial biomass N (-12%) and the N:P ratio. The C:N and N:P ratios of plant leaves were more sensitive to medium DPPT than to IPPT because drought increased plant N content, particularly in humid areas. The responses of plant and soil C:N:P stoichiometry to altered precipitation did not fit the double asymmetry model with a positive asymmetry under IPPT and a negative asymmetry under extreme DPPT. Soil microorganisms were more sensitive to IPPT than to DPPT, but they were more sensitive to extreme DPPT than extreme IPPT, consistent with the double asymmetry model. Soil microorganisms maintained stoichiometric homeostasis, whereas N:P ratios of plants follow that of the soils under altered precipitation. In conclusion, specific N allocation strategies of plants and microbial communities as well as N and P availability in soil critically mediate C:N:P stoichiometry by altered precipitation that need to be considered by prediction of ecosystem functions and C cycling under future climate change scenarios.

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.

Habitats modulate influencing factors shaping the spatial distribution of bacterial communities along a Tibetan Plateau riverine wetland

The Tibetan Plateau riverine wetland is very sensitive to global climate change. Understanding the mechanisms that maintain the spatial patterns of bacterial communities provides insight into the dominant biogeochemical processes within the plateau riverine wetlands. Nonetheless, the spatial distribution of bacterial communities along these wetlands has rarely been explored. We investigated the spatial patterns of bacterial community within rhizosphere soil, bulk soil, and sediment samples collected along the Yarlung Tsangpo riverine wetland (YTRW), the longest plateau riverine wetland in China. Our results indicated that the diversity of bacterial communities in all three habitats increased significantly along the YTRW. The slope of the linear relationship between distance and bacterial community diversity in sediment was steeper than those for bulk and rhizosphere soils. Furthermore, bacterial communities in all three habitats showed significant distance-decay relationships. A combination of historical factors (geographical distance and climatic factors) and contemporary environmental heterogeneity (edaphic properties) controlled spatial distributions of bacterial communities in all three habitats, although climatic factors were predominant. Climatic factors affected rhizosphere bacterial communities more than those in bulk soil and sediment. Co-occurrence network analysis revealed that the potential interactions between bacterial taxa may decrease along the YTRW. This field investigation highlighted that the climatic factors strongly influenced the spatial distribution of bacterial communities along the YTRW; however, habitat differences among rhizosphere soil, bulk soil, and sediment samples affected the relative importance of climatic factors on spatial distributions of the associated bacterial communities. These findings would improve the understanding of biogeochemical processes in these typical habitats and potential alterations provoked by climate change.

Significant effects of precipitation frequency on soil respiration and its components-A global synthesis

Global warming intensifies the hydrological cycle, which results in changes in precipitation regime (frequency and amount), and will likely have significant impacts on soil respiration (R_s ). Although the responses of R_s to changes in precipitation amount have been extensively studied, there is little consensus on how R_s will be affected by changes in precipitation frequency (PF) across the globe. Here, we synthesized the field observations from 296 published papers to quantify the effects of PF on R_s and its components using meta-analysis. Our results indicated that the effects of PF on R_s decreased with an increase in background mean annual precipitation. When the data were grouped by climate conditions, increased PF showed positive effects on R_s under the arid condition but not under the semi-humid or humid conditions, whereas decreased PF suppressed R_s across all the climate conditions. The positive effects of increased PF mainly resulted from the positive response of heterotrophic respiration under the arid condition while the negative effects of decreased PF were mainly attributed to the reductions in root biomass and respiration. Overall, our global synthesis provided for the first time a comprehensive analysis of the divergent effects of PF on R_s and its components across climate regions. This study also provided a framework for understanding and modeling responses of ecosystem carbon cycling to global precipitation change.

Decreased precipitation reduced the complexity and stability of bacterial co-occurrence patterns in a semiarid grassland

Introduction

Grasslands harbor complex bacterial communities, whose dynamic interactions are considered critical for organic matter and nutrient cycling. However, less is known about how changes in precipitation impact bacterial interactions.

Methods

We conducted precipitation manipulation experiments in the Eastern Eurasian Steppe in China and constructed co-occurrence networks for bacterial communities.

Results

The network topological features of the bacterial communities exhibited considerable differences among increased precipitation, control, and decreased precipitation gradients. The bacterial co-occurrence pattern in the increased precipitation gradient was the most complex and stable, with a large network size, followed by those of the control and decreased precipitation gradients. Soil moisture (SM) was the primary factor influencing the complexity, size, and stability of bacterial networks across different precipitation gradients, followed by total nitrogen (TN), belowground biomass, aboveground biomass, and total carbon (TC).

Discussion

Our results indicate that drought conditions reduce the complexity and stability of the bacterial community, and future changes in precipitation will greatly reshape bacterial interactions in semiarid grasslands. Overall, these findings could enhance our understanding of how microbes respond to changing precipitation patterns by regulating their interactions in water-limited ecosystems and will improve our ability to predict the impacts of precipitation regime change on ecosystem nutrient cycling and feedback between ecosystem processes and global climate change.

Nitrogen deposition experiment mimicked with NH4NO3 overestimates the effect on soil microbial community composition and functional potential in the Eurasian steppe

BACKGROUND

The nitrogenous compound deposited from the atmosphere to the soil is complex, but most field experiments mimic nitrogen deposition with the acid NH4NO3 alone. Thus, whether the acid and non-acid nitrogenous compounds have similar effects on biodiversity and ecosystem functions remains understudied. We mimicked nitrogen deposition with acidic NH4NO3 and (NH4)2SO4, and non-acidic urea, slow-released urea and NH4HCO3 in a temperate steppe, and quantified soil microbial taxonomic and functional gene composition with amplicon sequencing and shotgun metagenomics, respectively.

RESULTS

While NH4NO3 and (NH4)2SO4 significantly altered the soil microbial taxonomic and functional composition as well as their carbon decomposition potential, the other three compounds had smaller effects.

CONCLUSION

Our results suggested that previous nitrogen deposition experiments mimicked with NH4NO3 or (NH4)2SO4 alone may have overestimated the effect on biodiversity and ecosystem functions in the Eurasian steppe and similar ecosystems affected by mainly nonacidic nitrogen deposition.

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.

Realistic rates of nitrogen addition increase carbon flux rates but do not change soil carbon stocks in a temperate grassland

Changes in the biosphere carbon (C) sink are of utmost importance given rising atmospheric CO₂ levels. Concurrent global changes, such as increasing nitrogen (N) deposition, are affecting how much C can be stored in terrestrial ecosystems. Understanding the extent of these impacts will help in predicting the fate of the biosphere C sink. However, most N addition experiments add N in rates that greatly exceed ambient rates of N deposition, making inference from current knowledge difficult. Here, we leveraged data from a 13-year N addition gradient experiment with addition rates spanning realistic rates of N deposition (0, 1, 5, and 10 g N m^-2  year^-1 ) to assess the rates of N addition at which C uptake and storage were stimulated in a temperate grassland. Very low rates of N addition stimulated gross primary productivity and plant biomass, but also stimulated ecosystem respiration such that there was no net change in C uptake or storage. Furthermore, we found consistent, nonlinear relationships between N addition rate and plant responses such that intermediate rates of N addition induced the greatest ecosystem responses. Soil pH and microbial biomass and respiration all declined with increasing N addition indicating that negative consequences of N addition have direct effects on belowground processes, which could then affect whole ecosystem C uptake and storage. Our work demonstrates that experiments that add large amounts of N may be underestimating the effect of low to intermediate rates of N deposition on grassland C cycling. Furthermore, we show that plant biomass does not reliably indicate rates of C uptake or soil C storage, and that measuring rates of C loss (i.e., ecosystem and soil respiration) in conjunction with rates of C uptake and C pools are crucial for accurately understanding grassland C storage.

Organic mulch can suppress litchi downy blight through modification of soil microbial community structure and functional potentials

BACKGROUND

Organic mulch is an important management practice in agricultural production to improve soil quality, control crop pests and diseases and increase the biodiversity of soil microecosystem. However, the information about soil microbial diversity and composition in litchi plantation response to organic mulch and its attribution to litchi downy blight severity was limited. This study aimed to investigate the effect of organic mulch on litchi downy blight, and evaluate the biodiversity and antimicrobial potential of soil microbial community of litchi plantation soils under organic mulch.

RESULTS

Organic mulch could significantly suppress the disease incidence in the litchi plantation, and with a reduction of 37.74% to 85.66%. As a result of high-throughput 16S rRNA and ITS rDNA gene illumine sequencing, significantly higher bacterial and fungal community diversity indexes were found in organic mulch soils, the relative abundance of norank f norank o Vicinamibacterales, norank f Vicinamibacteraceae, norank f Xanthobacteraceae, Unclassified c sordariomycetes, Aspergillus and Thermomyces were significant more than that in control soils. Isolation and analysis of antagonistic microorganism showed that 29 antagonistic bacteria strains and 37 antagonistic fungi strains were unique for mulching soils.

CONCLUSIONS

Thus, we believe that organic mulch has a positive regulatory effect on the litchi downy blight and the soil microbial communities, and so, is more suitable for litchi plantation.

Effect of Nitrogen Addition on Soil Microbial Functional Gene Abundance and Community Diversity in Permafrost Peatland

Nitrogen is the limiting nutrient for plant growth in peatland ecosystems. Nitrogen addition significantly affects the plant biomass, diversity and community structure in peatlands. However, the response of belowground microbe to nitrogen addition in peatland ecosystems remains largely unknown. In this study, we performed long-term nitrogen addition experiments in a permafrost peatland in the northwest slope of the Great Xing'an Mountains. The four nitrogen addition treatments applied in this study were 0 g N·m-2·year-1 (CK), 6 g N·m-2·year-1 (N1), 12 g N·m-2·year-1 (N2), and 24 g N·m-2·year-1 (N3). Effects of nitrogen addition over a period of nine growing seasons on the soil microbial abundance and community diversity in permafrost peatland were analyzed. The results showed that the abundances of soil bacteria, fungi, archaea, nitrogen-cycling genes (nifH and b-amoA), and mcrA increased in N1, N2, and N3 treatments compared to CK. This indicated that nitrogen addition promoted microbial decomposition of soil organic matter, nitrogen fixation, ammonia oxidation, nitrification, and methane production. Moreover, nitrogen addition altered the microbial community composition. At the phylum level, the relative abundance of Proteobacteria increased significantly in the N2 treatment. However, the relative abundances of Actinobacteria and Verrucifera in the N2 treatment and Patescibacteria in the N1 treatment decreased significantly. The heatmap showed that the dominant order composition of soil bacteria in N1, N2, and N3 treatments and the CK treatment were different, and the dominant order composition of soil fungi in CK and N3 treatments were different. The N1 treatment showed a significant increase in the Ace and Chao indices of bacteria and Simpson index of fungi. The outcomes of this study suggest that nitrogen addition altered the soil microbial abundance, community structure, and diversity, affecting the soil microbial carbon and nitrogen cycling in permafrost peatland. The results are helpful to understand the microbial mediation on ecological processes in response to N addition.

Liming improves the stability of soil microbial community structures against the application of digestate made from dairy wastes

Lime is used to reduce soil acidification in agricultural soils. However, its effects on the soil microbial community are not well understood. Additionally, the soil microbial community is known to be influenced by fertilizers. However, the question remains whether liming influences the magnitude of fertilizers' impact on soil microbial communities. Therefore, an incubation experiment was performed to understand the effect of lime application (pH = 6.5 and 5.5 for the soils with and without lime, respectively) and fertilizer (digestate, urea and control) on the soil microbial community structures, stability and gene functions. Soils were sampled weekly after the application of fertilizers for a month. For microbial community analysis, DNA was extracted and sequenced targeting 16 S rRNA region. For gene abundances i.e 16 S rRNA, ammonia oxidizing archaea (AOA), ammonia oxidizing bacteria (AOB), nitrous oxide reductase (nosZ) and nitrite reductase (nirS) quantitative PCR was conducted. In results, the relative abundance of Actinobacteria was influenced more strongly by digestate in lime soils, while Alphaproteobacteria was influenced more strongly by digestate in the no lime soil. In NL treatments, digestate had a significant effect on more operational taxonomic units (146) compared to lime (127), indicating that lime application increased soil microbial community's stability. Liming and fertilizer had a significant effect on 16 S rRNA gene copy numbers with the highest values observed in lime plus digestate treatments. Soil pH had a significant effect on AOA, nosZ and nirS gene copy numbers with the highest values observed in lime treatments. In the lime treatments digestate application had a positive impact on AOB gene copy numbers but this was not the case for soils without liming treatments. These results indicate that soil pH and fertilizer type should be taken into consideration for the management of functional gene abundance in agricultural soils.

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.

Impact of land use on soil function and bacterial community in the Brazilian savanna

Land use systems have a great impact on soil function and microbial diversity in tropical soils. Our study aimed to evaluate soil biochemical indicators and community composition and to assess the relationship between soil biochemical and microbial indicators and bacterial diversity of three agroecosystems (pine forest, soya and sugarcane) and native Cerrado forest in the Brazilian savanna. Soil biochemical indicators (soil organic matter and enzymes) and high-throughput sequencing of 16S rDNA were performed in two topsoil depths (0-5 cm and 5-10 cm). Soil microbial and enzyme activity showed that agricultural soil usage has a negative impact on soil function compared to native and pine forests. Results also revealed higher enzyme activities in 0-5 cm depth compared to 5-10 cm depth, but enzymatic activities depend on land use systems. Soil bacterial community was affected by land use systems and depth, revealing changes in structure and abundance of bacterial composition. Alpha-diversity indexes were higher in the agricultural systems than in the forests, however they showed a significant negative correlation with most of the studied soil microbial and biochemical indicators. Our research had brought new relevant information about the relationship between the soil biochemical indicators and the bacterial diversity in the Brazilian Cerrado.

Fresh Compost Tea Application Does Not Change Rhizosphere Soil Bacterial Community Structure, and Has No Effects on Soybean Growth or Yield

Soil bacteria drive key ecosystem functions, including nutrient mobilization, soil aggregation and crop bioprotection against pathogens. Bacterial diversity is thus considered a key component of soil health. Conventional agriculture reduces bacterial diversity in many ways. Compost tea has been suggested as a bioinoculant that may restore bacterial community diversity and promote crop performance under conventional agriculture. Here, we conducted a field experiment to test this hypothesis in a soybean-maize rotation. Compost tea application had no influence on bacterial diversity or community structure. Plant growth and yield were also unresponsive to compost tea application. Combined, our results suggest that our compost tea bacteria did not thrive in the soil, and that the positive impacts of compost tea applications reported elsewhere may be caused by different microbial groups (e.g., fungi, protists and nematodes) or by abiotic effects on soil (e.g., contribution of nutrients and dissolved organic matter). Further investigations are needed to elucidate the mechanisms through which compost tea influences crop performance.

Do Aerial Nitrogen Depositions Affect Fungal and Bacterial Communities of Oak Leaves?

The amount of nitrogen (N) deposition onto forests has globally increased and is expected to double by 2050, mostly because of fertilizer production and fossil fuel burning. Several studies have already investigated the effects of N depositions in forest soils, highlighting negative consequences on plant biodiversity and the associated biota. Nevertheless, the impact of N aerial inputs deposited directly on the tree canopy is still unexplored. This study aimed to investigate the influence of increased N deposition on the leaf-associated fungal and bacterial communities in a temperate forest dominated by Sessile oak [Quercus petraea (Matt.) Liebl.]. The study area was located in the Monticolo forest (South Tyrol, Italy), where an ecosystem experiment simulating an increased N deposition has been established. The results highlighted that N deposition affected the fungal beta-diversity and bacterial alpha-diversity without affecting leaf total N and C contents. We found several indicator genera of both fertilized and natural conditions within bacteria and fungi, suggesting a highly specific response to altered N inputs. Moreover, we found an increase of symbiotrophic fungi in N-treated, samples which are commonly represented by lichen-forming mycobionts. Overall, our results indicated that N-deposition, by increasing the level of bioavailable nutrients in leaves, could directly influence the bacterial and fungal community diversity.

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

Currently, the impact of changes in precipitation and increased nitrogen(N) deposition on ecosystems has become a global problem. In this study, we conducted a 8-year field experiment to evaluate the effects of interaction between N deposition and precipitation change on soil bacterial communities in a desert steppe using high-throughput sequencing technology. The results revealed that soil bacterial communities were sensitive to precipitation addition but were highly tolerant to precipitation reduction. Reduced precipitation enhanced the competitive interactions of soil bacteria and made the ecological network more stable. Nitrogen addition weakened the effect of water addition in terms of soil bacterial diversity and community stability, and did not have an interactive influence. Moreover, decreased precipitation and increased N deposition did not have a superimposed effect on soil bacterial communities in the desert steppe. Soil pH, moisture content, and NH₄⁺-N and total carbon were significantly related to the structure of bacterial communities in the desert steppe. Based on network analysis and relative abundance, we identified Actinobacteria, Proteobacteria, Acidobacteria and Cyanobacteria members as the most important keystone bacteria that responded to precipitation changes and N deposition in the soil of the desert steppe. In summary, we comprehensively analyzed the responses of the soil bacterial community to precipitation changes and N deposition in a desert steppe, which provides a model for studying the effects of ecological factors on bacterial communities worldwide.

Nutrient availability is a dominant predictor of soil bacterial and fungal community composition after nitrogen addition in subtropical acidic forests

Nutrient addition to forest ecosystems significantly influences belowground microbial diversity, community structure, and ecosystem functioning. Nitrogen (N) addition in forests is common in China, especially in the southeast region. However, the influence of N addition on belowground soil microbial community diversity in subtropical forests remains unclear. In May 2018, we randomly selected 12 experimental plots in a Pinus taiwanensis forest within the Daiyun Mountain Nature Reserve, Fujian Province, China, and subjected them to N addition treatments for one year. We investigated the responses of the soil microbial communities and identified the major elements that influenced microbial community composition in the experimental plots. The present study included three N treatments, i.e., the control (CT), low N addition (LN, 40 kg N ha^-1 yr^-1), and high N addition (HN, 80 kg N ha^-1 yr^-1), and two depths, 0−10 cm (topsoil) and 10−20 cm (subsoil), which were all sampled in the growing season (May) of 2019. Soil microbial diversity and community composition in the topsoil and subsoil were investigated using high-throughput sequencing of bacterial 16S rDNA genes and fungal internal transcribed spacer sequences. According to our results, 1) soil dissolved organic carbon (DOC) significantly decreased after HN addition, and available nitrogen (AN) significantly declined after LN addition, 2) bacterial α-diversity in the subsoil significantly decreased with HN addition, which was affected significantly by the interaction between N addition and soil layer, and 3) soil DOC, rather than pH, was the dominant environmental factor influencing soil bacterial community composition, while AN and MBN were the best predictors of soil fungal community structure dynamics. Moreover, N addition influence both diversity and community composition of soil bacteria more than those of fungi in the subtropical forests. The results of the present study provide further evidence to support shifts in soil microbial community structure in acidic subtropical forests in response to increasing N deposition.

Soil prokaryotic community shows no response to 2 years of simulated nitrogen deposition in an arid ecosystem in northwestern China

An arid ecosystem might be sensitive to nitrogen (N) deposition, but the associated ecosystem-specific response of soil microbes is not well studied. To assess the N enrichment effects on plant and prokaryotic community diversity, we performed a two-year NH₄ NO₃ treatment in a desert steppe in northwestern China. Results showed that N addition increased plant aboveground biomass and decreased plant Shannon diversity. A C₄ herb (Salsola collina) became dominant, and loss of legume species was observed. The concentrations of soil NH₄ ⁺ -N, NO₃ ^- -N, microbial biomass N, and the plant aboveground biomass N pool increased in contrast to total N, suggesting that the N input into the arid ecosystem might mainly be assimilated by plants and exit the ecosystem. Remarkably, the α-diversity and structure of the soil prokaryotic community did not vary even at the highest N addition rate. Structural equation modelling further found that the plant aboveground N pool counteracted the acidification effect of N deposition and maintained soil pH thus partially stabilizing the composition of prokaryotic communities in a desert steppe. These findings suggested that the plants and N loss might contribute to the lack of responsiveness of soil prokaryotic community to N deposition in a desert steppe.

Phosphorus Reduces Negative Effects of Nitrogen Addition on Soil Microbial Communities and Functions

Increased soil nitrogen (N) from atmospheric N deposition could change microbial communities and functions. However, the underlying mechanisms and whether soil phosphorus (P) status are responsible for these changes still have not been well explained. Here, we investigated the effects of N and P additions on soil bacterial and fungal communities and predicted their functional compositions in a temperate forest. We found that N addition significantly decreased soil bacterial diversity in the organic (O) horizon, but tended to increase bacterial diversity in the mineral (A) horizon soil. P addition alone did not significantly change soil bacterial diversity but mitigated the negative effect of N addition on bacterial diversity in the O horizon. Neither N addition nor P addition significantly influenced soil fungal diversity. Changes in soil microbial community composition under N and P additions were mainly due to the shifts in soil pH and NO3- contents. N addition can affect bacterial functional potentials, such as ureolysis, N fixation, respiration, decomposition of organic matter processes, and fungal guilds, such as pathogen, saprotroph, and mycorrhizal fungi, by which more C probably was lost in O horizon soil under increased N deposition. However, P addition can alleviate or switch the effects of increased N deposition on the microbial functional potentials in O horizon soil and may even be a benefit for more C sequestration in A horizon soil. Our results highlight the different responses of microorganisms to N and P additions between O and A horizons and provides an important insight for predicting the changes in forest C storage status under increasing N deposition in the future.

Pioneer trees of Betula pendula at a red gypsum landfill harbour specific structure and composition of root-associated microbial communities

The study of root-associated microbial communities is important to understand the natural processes involved in plant recolonisation at degraded areas. Root associated bacterial and fungal communities of woody species colonising a red gypsum landfill (a metal-enriched environment) were characterised through metabarcoding. Among trees naturally growing on the landfill, Betula pendula is the only tree species in the centre of the area, whereas companion tree species such as Populus nigra, P. tremula and Salix purpurea were present on the edges. The bacterial community was dominated by Proteobacteria (38%), Actinobacteria (35%) and Bacteroidetes (20%) and the most abundant bacterial OTU belonged to the family Streptomycetaceae. The fungal community was dominated by Ascomycota (60%) and Basidiomycota (30%) and the most abundant family was Pyronemataceae. Analysis of similarities, heatmap and hierarchical cluster analysis showed that B. pendula grown in the centre of the landfill harboured a specific microbial community, which was unique and different, not only from other tree species (Populus or Salix spp.), but also from other B. pendula growing at the edges. Our findings on relevant indicator OTUs associated to the birches located in the centre of the landfill (such as Otu00716 Catellatospora sp. (family Micromonosporaceae, phylum Actinobacteria) or Otu4_35502 Russula sp. (family Russulaceae, phylum Basidiomycota)) may have important implications for the successful revegetation of these harsh environments using microbial-based phytostabilisation approaches.

Critical transition of soil bacterial diversity and composition triggered by nitrogen enrichment

Soil bacterial communities are pivotal in regulating terrestrial biogeochemical cycles and ecosystem functions. The increase in global nitrogen (N) deposition has impacted various aspects of terrestrial ecosystems, but we still have a rudimentary understanding of whether there is a threshold for N input level beyond which soil bacterial communities will experience critical transitions. Using high-throughput sequencing of the 16S rRNA gene, we examined soil bacterial responses to a long-term (13 yr), multi-level, N addition experiment in a temperate steppe of northern China. We found that plant diversity decreased in a linear fashion with increasing N addition. However, bacterial diversity responded nonlinearly to N addition, such that it was unaffected by N input below 16 g N·m^-2 ·yr^-1 , but decreased substantially when N input exceeded 32 g N·m^-2 ·yr^-1 . A meta-analysis across four N addition experiments in the same study region further confirmed this nonlinear response of bacterial diversity to N inputs. Substantial changes in soil bacterial community structure also occurred between N input levels of 16 to 32 g N·m^-2 ·yr^-1 . Further analysis revealed that the loss of soil bacterial diversity was primarily attributed to the reduction in soil pH, whereas changes in soil bacterial community were driven by the combination of increased N availability, reduced soil pH, and changes in plant community structure. In addition, we found that N addition shifted bacterial communities toward more putatively copiotrophic taxa. Overall, our study identified a threshold of N input level for bacterial diversity and community composition. The nonlinear response of bacterial diversity to N input observed in our study indicates that although bacterial communities are resistant to low levels of N input, further increase in N input could trigger a critical transition, shifting bacterial communities to a low-diversity state.

Bacterial Community Structure and Predicted Function in Wheat Soil From the North China Plain Are Closely Linked With Soil and Plant Characteristics After Seven Years of Irrigation and Nitrogen Application

The influence of water and nitrogen (N) management on wheat have been investigated, but studies on the impact of long-term interactive water and N management on microbial structure and function are limited. Soil chemical properties and plants determine the soil microbial communities whose functions involved in nutrient cycling may affect plant productivity. There is an urgent need to elucidate the underlying mechanisms to optimize these microbial communities for agricultural sustainability in the winter wheat production area of the North China Plain. We performed high-throughput sequencing and quantitative PCR of the 16S rRNA gene on soil from a 7-year-old stationary field experiment to investigate the response of bacterial communities and function to water and N management. It was observed that water and N management significantly influenced wheat growth, soil properties and bacterial diversity. N application caused a significant decrease in the number of operational taxonomic units (OTUs), and both Richness and Shannon diversity indices, in the absence of irrigation. Irrigation led to an increase in the relative abundance of Planctomycetes, Latescibacteria, Anaerolineae, and Chloroflexia. In addition, most bacterial taxa were correlated with soil and plant properties. Some functions related to carbohydrate transport, transcription, inorganic ion transport and lipid transport were enriched in irrigation treatment, while N enriched predicted functions related to amino acid transport and metabolism, signal transduction, and cell wall/membrane/envelope biogenesis. Understanding the impact of N application and irrigation on the structure and function of soil bacteria is important for developing strategies for sustainable wheat production. Therefore, concurrent irrigation and N application may improve wheat yield and help to maintain those ecosystem functions that are driven by the soil microbial community.

Responses of soil extracellular enzyme activities and microbial community properties to interaction between nitrogen addition and increased precipitation in a semi-arid grassland ecosystem

Both atmospheric nitrogen (N) deposition and precipitation can strongly impact below-ground biogeochemical processes. Soil extracellular enzymes activities (EEAs) and microorganisms are considered as the key agents in ecosystem nutrient cycling. However, how the interaction between increasing N deposition and precipitation may affect soil EEAs and microbes remain poorly understood. In a 5-year field experiment in a meadow steppe in northern China, we tested the effects of N addition (N0, 0; N1, 5; N2, 10 g N m^-2 yr^-1) and increased precipitation (W0, ambient precipitation; W1, increase of 15% ambient precipitation; W2, increase of 30% ambient precipitation) on soil EEAs, microbial and chemical properties. Results showed that their interaction significantly affected all hydrolase activities, except for β-1,4-xylosidase (βX). Furthermore, increased precipitation and N addition interactively affected bacterial gene copies (P ≤ 0.05), and increased precipitation comparatively had a stronger effects. The results on the combination of N addition and increased precipitation showed that increased precipitation alleviated the positive effects of N addition on soil EEAs. This implies that the effects of either treatment alone on grassland biogeochemical processes may be alleviated by their simultaneous occurrence. Our results suggested that soil EEAs were mainly controlled by the content of N and phosphorus (P), and the ratio of C: N and C: P. Therefore, soil element content and stoichiometry could better explain the responses of EEAs to global changes. Moreover, soil microbial communities were mainly controlled by soil P content. Overall, our study highlights that the interaction between N deposition and precipitation may play a vital role in predicting the responses of soil enzyme activities to global changes in grassland ecosystems.

Effects of precipitation changes on soil bacterial community composition and diversity in the Junggar desert of Xinjiang, China

Variation in precipitation can markedly affect the structure and function of soil microbial communities, especially in arid areas which are limited by water resources. Therefore, it is critical to understand how soil bacterial community composition and diversity will respond to variation in precipitation. In this study, we examined the soil bacterial community structure and diversity between five precipitation treatments (60% decrease, 30% decrease, control, 30% increase and 60% increase in precipitation) in the same arid site, in the Junggar desert of Xinjiang, northern China. The dominant bacterial phyla, present at similar frequencies in plots with different precipitation levels, were Actinobacteria, Proteobacteria, Bacteroidetes, Acidobacteria and Chloroflexi. The Shannon-Wiener and Chao1 indices of soil bacterial α-diversity were both positively correlated with plant diversity. Our results indicated that (1) extreme drought significantly decreased bacterial abundance and diversity compared with increased precipitation; (2) variation in precipitation did not change the dominant components of the bacterial communities; and (3) soil pH and total nitrogen concentration were the key factors affecting soil bacterial composition in the Junggar desert.

Effect of coupled reduced irrigation and nitrogen fertilizer on soil mite community composition in a wheat field

Groundwater and nitrogen fertilizer overuse severely threatens crop productions; thus, current ecological agriculture requires low irrigation and nitrogen fertilizer inputs. The effects of combined reduced irrigation and nitrogen fertilizer addition on soil organism (e.g., mite) community and biodiversity remain poorly understood. We analyzed soil mite community composition, wheat grain yield, and soil characteristics in a 10-year manipulation experiment with two levels of irrigation (reduced and conventional irrigation) and five nitrogen fertilizer levels (0, 70, 140, 210, and 280 kg N/ha). Reduced irrigation (20% reduction, from 280 to 220 mm) and nitrogen fertilizer (25% reduction, from 280 to 210 kg N/ha) addition did not significantly influence soil mite community and wheat yield. The relative abundances of fungivores and predators showed negative quadratic relationships with wheat yield, while that of plant parasites showed a positive relationship. The relationships between soil mite trophic groups and wheat yield revealed that we can evaluate the impacts of reduced irrigation and nitrogen fertilizer addition from the perspective of soil fauna. Soil mite community composition was altered by soil abiotic factors prior to reduced irrigation and nitrogen fertilizer addition. Overall, moderate reductions of irrigation and nitrogen fertilizer may not threaten to soil mite community and diversity or decrease crop production; in contrast, such reductions will benefit mite community development and the sustainable agriculture.

Biogeographic Patterns and Assembly Mechanisms of Bacterial Communities Differ Between Habitat Generalists and Specialists Across Elevational Gradients

A core issue in microbial ecology is the need to elucidate the ecological processes and underlying mechanisms involved in microbial community assembly. However, the extent to which these mechanisms differ in importance based on traits of taxa with different niche breadth is poorly understood. Here, we used high-throughput sequencing to examine the relative importance of environmental selection and stochastic processes in shaping soil bacterial sub-communities with different niche breadth (including habitat generalists, specialists and other taxa) across elevational gradients on the subalpine slope of Mount Wutai, Northern China. Our findings suggested that the composition of soil bacterial communities differed significantly different among elevational gradients. According to the niche breadth index, 10.9% of OTUs were defined as habitat generalists (B-value >8.7) and 10.0% of OTUs were defined as habitat specialists (B-value <1.5). Generalists and specialists differed distinctly in diversity and biogeographic patterns across elevational gradients. Environmental selection (deterministic processes) and spatial factors (stochastic processes) seemed to determine the assembly and biogeography of habitat generalists. However, for specialists, deterministic processes strongly influenced the distribution, while stochastic processes were not at play. Environmental drivers for generalists and specialists differed, as did their importance. Elevation, total nitrogen and pH were the main factors determining habitat generalists, and soil water content, nitrate nitrogen and pH had the strongest impacts on specialists. Moreover, variation partitioning analysis revealed that environmental selection had a much greater impact on both generalists (17.7% of pure variance was explained) and specialists (3.6%) than spatial factors. However, generalists had a much stronger response to spatial factors (2.3%) than specialists (0.3%). More importantly, null models of β-diversity suggested that specialists deviated significantly from non-neutral assembly mechanisms (relative null deviation= 0.64–0.74) relative to generalists (0.16–0.65) (P < 0.05). These results indicate that generalists and specialists are governed by different assembly mechanisms and present distinct biogeographical patterns. The large proportion of unexplained variation in specialists (93.3%) implies that very complex assembly mechanisms exist in the assembly of specialists across elevational gradients on the subalpine slope of Mount Wutai. It is essential to understand the microbial community assembly at a more refined level, and to expand the current understanding of microbial ecological mechanisms.

Increasing atmospheric deposition nitrogen and ammonium reduced microbial activity and changed the bacterial community composition of red paddy soil

Atmospheric deposition nitrogen (ADN) increases the N content in soil and subsequently impacts microbial activity of soil. However, the effects of ADN on paddy soil microbial activity have not been well characterized. In this study, we studied how red paddy soil microbial activity responses to different contents of ADN through a 10-months ADN simulation on well managed pot experiments. Results showed that all tested contents of ADN fluxes (27, 55, and 82kgNha^-1 when its ratio of NH₄⁺/NO₃^--N (R_N) was 2:1) enhanced the soil enzyme activity and microbial biomass carbon and nitrogen and 27kgNha^-1 ADN had maximum effects while comparing with the fertilizer treatment. Generally, increasing of both ADN flux and R_N (1:2, 1:1 and 2:1 with the ADN flux of 55kgNha^-1) had similar reduced effects on microbial activity. Furthermore, both ADN flux and R_N significantly reduced soil bacterial alpha diversity (p<0.05) and altered bacterial community structure (e.g., the relative abundances of genera Dyella and Rhodoblastus affiliated to Proteobacteria increased). Redundancy analysis demonstrated that ADN flux and R_N were the main drivers in shaping paddy soil bacteria community. Overall, the results have indicated that increasing ADN flux and ammonium reduced soil microbial activity and changed the soil bacterial community. The finding highlights how paddy soil microbial community response to ADN and provides information for N management in paddy soil.

Ammonium nitrogen content is a dominant predictor of bacterial community composition in an acidic forest soil with exogenous nitrogen enrichment

Soil pH is a dominant factor affecting bacterial community composition in acidic, neutral, and alkaline soils but not in severely acidic soils (pH<4.5). We conducted a nitrogen (N) addition experiment in the field in severely acidic forest soil to determine the response of the soil bacterial community and identified the dominant factor in determining community composition. Using a high-throughput Illumina HiSeq sequencing platform, we found that high levels of N addition significantly decreased soil bacterial diversity and altered the composition of the soil bacterial community. The addition of nitrogen increased the relative abundance of copiotrophic taxa (Proteobacteria and Actinobacteria phyla) but decreased the relative abundance of oligotrophic taxa (Acidobacteria, Verrucomicrobia, Planctomycetes, and WD272). In particular, the relative abundance of N-cycling-related microbes (e.g., Burkholderia and Rhizomicrobium genera) also increased upon addition of N. Our correlation analysis showed that soil ammonium nitrogen concentration, rather than pH or nitrate nitrogen concentration, was a key environmental parameter determining the composition of the soil bacterial community. However, these bacterial response behaviors were observed only in the dry season and not in the wet season, indicating that high temperature and precipitation in the wet season may alleviate the impact of the addition of N on soil bacterial diversity and community composition. These results suggest that the soil bacterial community shifted to copiotrophic taxa with higher N demands under increased N addition in severely acidic forest soil.

Enzyme activity and microbial biomass availability in artificial soils on rock-cut slopes restored with outside soil spray seeding (OSSS): Influence of topography and season

Large-scale railway construction has resulted in large areas of bare-cut-slope, and outside soil spray seeding (OSSS), a frequently used technique, has been adopted for slope restoration for many years. However, compared with natural slope soils, the quality of artificial soils on rock-cut slopes is low. Enzyme activity and microbial biomass are the main indices used for estimating soil quality; thus, our objective was to explore the influence of slope position, slope aspect, and season on two important factors that positively influence the plant growth capability in artificial soil. Further, we suggest modifications of the proportions of OSSS ingredients, not only to manage cut slopes more economically but also to provide a new framework for managing desertification. We chose a bare-cut-slope that had been restored five years ago near the Suiyu Railway (Chongqing-Suining), in Sichuan Province, China, as our study plot. Soil samples were collected at a depth of 10 cm. We conclude that natural slopes exhibited higher urease, sucrase, and catalase activity and higher microbial biomass than cut slopes. The protease and polyphenoloxidase enzyme activities and the microbial biomass were higher on the cut slopes in the months of October and January, with the highest protease activity in October, and the highest polyphenoloxidase activity in January. The enzyme activity and microbial biomass were always lower on lower slopes, with the exception of polyphenoloxidase activity. The slope aspect influenced soil enzyme activity, resulting in higher activity on north-facing slopes than on south-facing slopes. These results provided scientific support for artificial revegetation methods in an ecological context.

Resource Availability Drives Responses of Soil Microbial Communities to Short-term Precipitation and Nitrogen Addition in a Desert Shrubland

Desert microbes are expected to be substantially sensitive to global environmental changes, such as precipitation changes and elevated nitrogen deposition. However, the effects of precipitation changes and nitrogen enrichment on their diversity and community composition remain poorly understood. We conducted a field experiment over 2 years with multi-level precipitation and nitrogen addition in a desert shrubland of northern China, to examine the responses of soil bacteria and fungi in terms of diversity and community composition and to explore the roles of plant and soil factors in structuring microbial communities. Water addition significantly increased soil bacterial diversity and altered the community composition by increasing the relative abundances of stress-tolerant (dormant) taxa (e.g., Acidobacteria and Planctomycetes); however, nitrogen addition had no substantial effects. Increased precipitation and nitrogen did not impact soil fungal diversity, but significantly shifted the fungal community composition. Specifically, water addition reduced the relative abundances of drought-tolerant taxa (e.g., the orders Pezizales, Verrucariales, and Agaricales), whereas nitrogen enrichment decreased those of oligotrophic taxa (e.g., the orders Agaricales and Sordariales). Shifts in microbial community composition under water and nitrogen addition occurred primarily through changing resource availability rather than plant community. Our results suggest that water and nitrogen addition affected desert microbes in different ways, with watering shifting stress-tolerant traits and fertilization altering copiotrophic/oligotrophic traits of the microbial communities. These findings highlight the importance of resource availability in driving the desert microbial responses to short-term environmental changes.

Influences of Canopy Nitrogen and Water Addition on AM Fungal Biodiversity and Community Composition in a Mixed Deciduous Forest of China

Nitrogen (N) deposition and precipitation could profoundly influence the structure and function of forest ecosystems. However, conventional studies with understory additions of nitrogen and water largely ignored canopy-associated ecological processes and may have not accurately reflected the natural situations. Additionally, most studies only made sampling at one time point, overlooked temporal dynamics of ecosystem response to environmental changes. Here we carried out a field trial in a mixed deciduous forest of China with canopy addition of N and water for 4 years to investigate the effects of increased N deposition and precipitation on the diversity and community composition of arbuscular mycorrhizal (AM) fungi, the ubiquitous symbiotic fungi for the majority of terrestrial plants. We found that (1) in the 1st year, N addition, water addition and their interactions all exhibited significant influences on AM fungal community composition; (2) in the 2nd year, only water addition significantly reduced AM fungal alpha-diversity (richness and Shannon index); (3) in the next 2 years, both N addition and water addition showed no significant effect on AM fungal community composition or alpha-diversity, with an exception that water addition significantly changed AM fungal community composition in the 4th year; (4) the increment of N or water tended to decrease the abundance and richness of the dominant genus Glomus and favored other AM fungi. (5) soil pH was marginally positively related with AM fungal community composition dissimilarity, soil NH₄ ⁺-N and N/P showed significant/marginal positive correlation with AM fungal alpha-diversity. We concluded that the effect of increased N deposition and precipitation on AM fungal community composition was time-dependent, mediated by soil factors, and possibly related to the sensitivity and resilience of forest ecosystem to environmental changes.

Microbial Taxa Distribution Is Associated with Ecological Trophic Cascades along an Elevation Gradient

The elevational pattern of soil microbial diversity along mountain slopes has received considerable interest over the last decade. An increasing amount of taxonomic data on soil microbial community composition along elevation gradients have been collected, however the trophic patterns and environmental drivers of elevational changes remain largely unclear. Here, we examined the distribution patterns of major soil bacterial and fungal taxa along the northern slope of Changbai Mountain, Northeast China, at five typical vegetation types located between 740 and 2,691 m above sea level. Elevational patterns of the relative abundance of specific microbial taxa could be partially explained by the oligotrophic-copiotrophic theory. Specifically, two dark-coniferous forests, located at mid-elevation sites, were considered to be oligotrophic habitats, with relatively higher soil C/N ratio and [Formula: see text]-N concentrations. As expected, oligotrophic microbial taxa, belonging to the bacterial phyla Acidobacteria and Gemmatimonadetes, and fungal phylum Basidiomycota, were predominant in the two dark-coniferous forests, exhibiting a mid-elevation maximum pattern. In contrast, the broad leaf-Korean pine mixed forest located at the foot of the mountain, Betula ermanii-dominated forest located below the tree line, and alpine tundra at the highest elevation were considered more copiotrophic habitats, characterized by higher substrate-induced-respiration rates and [Formula: see text]-N concentrations. Microbial taxa considered to be so called copiotrophic members, such as bacterial phyla Proteobacteria and Actinobacteria, and fungal phylum Ascomycota, were relatively abundant in these locations, resulting in a mid-elevation minimum pattern. At finer taxonomic levels, the two most abundant proteobacterial classes, alpha- and beta-Proteobacteria, along with Acidobacteria Gp1, 2, 3, 15, and the Basidiomycotal class of Tremellomycetes were classified with the copiotrophic group. Gamma- and delta-Proteobacteria, Acidobacteria Gp4, 6, 7, 16, and Basidiomycotal class of Agaricomycetes were classified as oligotrophic taxa. This work uses the oligotrophic-copiotrophic theory to explain the elevational distribution pattern of the relative abundance of specific microbial taxa, confirming some of the existing trophic classifications of microbial taxa and expanding on the theory to include a broader range of taxonomic levels.