Alter Soil Microbial Community Research Articles

The effect of prescribed fires on abiotic and biotic factors in the southern region of Puerto Rico

Field fires can modify soil nutrient cycling and alter soil microbial communities (SMC), although the latter is not well understood. In the southern region of Puerto Rico, field fires have become a significant problem during the dry season. To mimic the effects of a field fire, we performed prescribed fires on a hillside at the Juana Díaz Agricultural Experiment substation in October 2015 and March 2017. A complete randomized block design was established in Yauco soil (Typic calciustolls) that included the following treatments: negative control (unburned), positive control (burned plots, no remediation), mulching treatment (burned plots remediated with Leucaena spp. mulch), and surfactant treatment (burned plots remediated with a surfactant). In the first burning (2015), soil samples were collected before burning and at 30, 180, and 420 days after burning (DAB). In the second burning (2017), soil samples were collected at 30, 90, and 270 DAb. soil physicochemical properties and microbial community structure were assessed using phospholipid fatty acid (PLFA) analysis. Overall, burning increased soil exchangeable Ca2+ (except after 30 DAB in the second burning) and decreased exchangeable K+ when compared to unburned soils. compared to unburned plots, total fungal PLFA was significantly lower in burned plots with or without mulch and surfactant treatments, and total bacterial PLFA did not differ between burned and unburned plots after 30 days. Total microbial biomass was significantly (P<0.05) higher in mulch and surfactant treated burned soil compared to unburned and burned plots without treatment after 90 DAB (2017) and 420 (2015) DAB. The use of mulch and surfactant treatments in prescribed burning fields increased microbial communities 90 DAB. This study emphasizes short-term changes in microbial communities and suggests they are highly resilient to disturbances after prescribed fires.

The response of soil respiration to land‐use change depends on soil microbial community being regulated by edaphic factors in the Loess Plateau, China

AbstractLand‐use change has significant influences on soil respiration (Rs) in terrestrial ecosystems. Soil microbes play critical roles in soil carbon cycling. Nevertheless, the specific mechanism of how changes in soil microbial properties are linked to the variation of Rs rate during land‐use change still remains poorly understood, especially in the Loess Plateau, China. Here, the characteristics of Rs rate and soil microbial community following the land‐use change from farmland to plantation/grassland were analyzed via an automated soil CO2 flux system and high‐throughput 16S rDNA gene sequencing. The afforestation altered soil microbial diversity and community composition, which was mainly explained by soil pH, temperature, organic matter, nitrate, alkali‐hydrolyzed nitrogen, and available phosphorus. The biomarkers of Bacteroidetes, Firmicutes, and Thaumarchaeota were found in farmland soil at the phylum level. The afforestation also significantly decreased Rs rate, which was closely related to Shannon's index, Simpson's index, and some microbial taxa, such as Bacteroidetes, Firmicutes, Nitrospirae, and Acidobacteria. Bacteroidetes, and Firmicutes were particularly expected to be important drivers of high Rs rate in farmland soil. Moreover, the microbial interaction was probably also an important factor affecting Rs rate. Our results indicate that the response of Rs to land‐use change depends on soil microbial community being regulated by soil physicochemical properties in the Loess Plateau, China.

Disturbance of eucalypt forests alters the composition, function, and assembly of soil microbial communities.

Forest disturbance has well-characterized effects on soil microbial communities in tropical and northern hemisphere ecosystems, but little is known regarding effects of disturbance in temperate forests of the southern hemisphere. To address this question, we collected soils from intact and degraded Eucalyptus forests along an east-west transect across Tasmania, Australia, and characterized prokaryotic and fungal communities using amplicon sequencing. Forest degradation altered soil microbial community composition and function, with consistent patterns across soil horizons and regions of Tasmania. Responses of prokaryotic communities included decreased relative abundance of Acidobacteriota, nitrifying archaea, and methane-oxidizing prokaryotes in the degraded forest sites, while fungal responses included decreased relative abundance of some saprotrophic taxa (e.g. litter saprotrophs). Forest degradation also reduced network connectivity in prokaryotic communities and increased the importance of dispersal limitation in assembling both prokaryotic and fungal communities, suggesting recolonization dynamics drive microbial composition following disturbance. Further, changes in microbial functional groups reflected changes in soil chemical properties-reductions in nitrifying microorganisms corresponded with reduced NO3-N pools in the degraded soils. Overall, our results show that soil microbiota are highly responsive to forest degradation in eucalypt forests and demonstrate that microbial responses to degradation will drive changes in key forest ecosystem functions.

Seasonality and bacterial community assembly processes dominate prairie ecosystem service disruption during invasion

Invasive plants alter soil microbial communities and ecosystem services reducing the Earth's carrying capacity for humans. Many ecosystem services are underpinned by soil microbial communities, and these communities arise from assembly processes that are likely altered by invasion. We evaluated the hypothesis that invasive effects on grassland ecosystem services arise from changes in microbial community assembly processes caused by invasion. We sampled 515 plots at a native Rough Fescue prairie undergoing invasion by nine invasive species of which smooth brome (Bromus inermis) is a dominant member. Each week, for 26 weeks, we monitored invasion effects on vascular plant communities, ecosystem services, as well as bacterial and fungal community structures. Invasive effects on ecosystem services interacted with seasonal (plant green-up, peak biomass, and plant senescence) effects and consistently disrupted ecosystem service provision. Invasion increased heterogenous selection in fungal communities but otherwise had minor effects on assembly process. Only ∼20% of community composition could be ascribed to deterministic filters which hindered our ability to conclusively link invasion to assembly processes. Assembly processes explained changes in ecosystem services with bacterial assembly accounting for 2.5% of food, 4% of climate, 9% of conservation and 5.5% of fertility services. Fungal communities were less consistent in their effects on ecosystem services with only food (3%) and water (4%) services influenced by fungal assembly. After seasonality (27%), bacterial assembly processes (4%) accounted for the largest effect on ecosystem services, overshadowing invasion (2%) and fungal assembly (2%). At this 130-ha site, after seasonal effects, bacterial assembly processes had the largest effect on ecosystem services with plant invasion placing a distant third.

Red imported fire ant nesting affects the structure of soil microbial community.

The red imported fire ants (RIFA, Solenopsis invicta) have become a well-known invasive species that poses significant ecological and economic threats globally. As of recent times, the geographic scope of its invasion in China is rapidly expanding, thereby aggravating the extent and severity of its detrimental effects. The importance of soil microorganisms for maintaining soil health and ecosystem function has been widely acknowledged. However, the negative impact of RIFAs on soil microbial communities and their functions has not yet been fully understood. In this study, we sequenced the V3-V4 variable region of the bacterial 16S rRNA gene in soil samples collected from three types of RIFA nests to investigate the impact of RIFA invasion on soil microbial diversity and composition. The results of alpha diversity analysis showed that the normal soil without nests of RIFAs exhibited the highest level of diversity, followed by the soil samples from RIFA-invaded nests and abandoned nests. Taxonomy and biological function annotation analyses revealed significant differences in microbial community structure and function among the different samples. Our findings demonstrate that RIFA invasion can significantly alter soil microbial community composition, which could ultimately affect ecosystem function. Therefore, effective management strategies are urgently needed to mitigate the negative impact of invasive species on native ecosystems.

Response of heavy-metal and antibiotic resistance genes and their related microbe in rice paddy irrigated with treated municipal wastewaters

Paddy irrigation with secondary effluents from municipal wastewater treatment plants (MWTPs) is a well-established practice to alleviate water scarcity. However, the reuse might lead to more complicated contamination caused by interactions between residual antibiotics in effluents and heavy metals in paddy soil. To date, no information is available for the potential effects of dual stress of heavy metals and antibiotics on heavy-metal resistance genes (MRGs) and antibiotic resistance genes (ARGs). Here, this study investigated the response of heavy metal and antibiotic resistance genes, and related microorganisms to the dual threat of antibiotics and heavy metals under the long-term MWTP effluent irrigation for rice paddy using metagenome. The results showed that there was not a negative effect on rice consumption if MWTP effluent was used to irrigate rice for a long time. The concentration of antibiotics could reshape the ARGs and MRG profiles in rice paddy soil. The findings revealed the co-occurrence of ARGs and MRGs in rice paddy soils, thus highlighting the need for simultaneous elimination of antibiotics and heavy metals to effectively reduce ARGs and MRGs. Acn and sul1 genes encoding Iron and sulfonamides resistance mechanisms are the most abundant MRG and ARG, respectively. Network analysis revealed the possibility that IntI1 plays a role in the co-transmission of MRG and ARG to host microbes, and that Proteobacteria are the most dominant hosts for MRG, ARG, and integrons. The presence of antibiotics in irrigated MWTP effluents has been found to stimulate the proliferation of heavy metal and antibiotic resistances by altering soil microbial communities. This study will enhance our comprehension of the co-selection between ARGs and MRGs, as well as reveal the concealed environmental impacts of combined pollution. The obtained results have important implications for food safety and human health in rice.

Urbanization reduces soil microbial network complexity and stability in the megacity of Shanghai

Urbanization is altering the co-occurrence networks of ecological communities that are critical to maintaining ecosystem functions and services. Soil microbial communities play key roles in various ecosystem processes, but how soil microbial co-occurrence networks respond to urbanization is unclear. Here we analyzed co-occurrence networks in soil archaeal, bacterial, and fungal communities from 258 soil sampling sites across the megacity of Shanghai along large urbanization gradients. We found that topological features of microbial co-occurrence networks were strongly altered by urbanization. In particular, microbial communities in more urbanized land-use and highly impervious land cover had less connected and more isolated network structures. These structural variations were accompanied by the dominance of connectors and module hubs affiliated with the Ascomycota in fungi and Chloroflexi in bacteria, and there were greater losses in efficiency and connectivity in urbanized than in remnant land-use in simulated disturbances. Furthermore, even though soil properties (especially soil pH and organic carbon) were major factors shaping topological features of the microbial networks, urbanization still uniquely explained a proportion of the variability, particularly those describing network connections. These results demonstrate that urbanization has clear direct and indirect effects on microbial networks and provide novel insights into how urbanization alters soil microbial communities.

Natural restoration alters soil microbial community structure, but has contrasting effects on the diversity of bacterial and fungal assemblages in salinized grasslands

Natural restoration has often been considered an effective measure for rehabilitating degraded ecosystems. However, its impact on the structure and diversity of soil microbial communities, particularly within a salinized grassland during its restoration succession, remains unclear. In this study, we examined the effects of natural restoration on the Shannon-Wiener diversity index, Operational Taxonomic Units (OTU) richness, and structure of the soil microbial community of a sodic-saline grassland in China using high-throughput amplicon sequencing data from representative successional chronosequences. Our results indicated that natural restoration resulted in a significant mitigation of the grassland salinization (pH from 9.31 to 8.32 and electrical conductivity from 393.33 to 136.67 μs·cm−1) and a significant alteration of the soil microbial community structure of the grassland (p < 0.01). However, the effects of natural recovery differed in terms of the abundance and diversity of bacteria and fungi. For example, the relative abundance of the bacterial phyla Acidobacteria increased by 116.45 % in the topsoil and 339.03 % in the subsoil, while that of the fungal phyla Ascomycota decreased by 8.86 % in the topsoil and 30.18 % in the subsoil. There was no significant effect of restoration on bacterial diversity, but fungal diversity increased by 15.02 % in the Shannon-Wiener index and 62.20 % in the OTU richness in the topsoil. Model-selection analysis further corroborated that the alteration of the soil microbial structure by natural restoration may be due to the fact that the bacteria could adapt to the alleviated salinized grassland soil and the fungi could adapt to the improved soil fertility of the grasslands. Overall, our results contribute to an in-depth understanding of the impacts of natural restoration on soil microbial diversity and community structure in salinized grasslands during the long-term successional course. This may also help to apply natural restoration as a greener practice option for managing degraded ecosystems.

Contrasting sensitivity of soil bacterial and fungal community composition to one year of water limitation in Scots pine mesocosms.

The soil microbiome is crucial for regulating biogeochemical processes and can thus strongly influence tree health, especially under stress conditions. However, little is known about the effect of prolonged water deficit on soil microbial communities during the development of saplings. We assessed the response of prokaryotic and fungal communities to different levels of experimental water limitation in mesocosms with Scots pine saplings. We combined analyses of physicochemical soil properties and tree growth with DNA metabarcoding of soil microbial communities throughout four seasons. Seasonal changes in soil temperature and soil water content and a decreasing soil pH strongly influenced the composition of microbial communities but not their total abundance. Contrasting levels of soil water contents gradually altered the soil microbial community structure over the four seasons. Results indicated that prokaryotic communities were less resistant to water limitation than fungal communities. Water limitation promoted the proliferation of desiccation-tolerant, oligotrophic taxa. Moreover, water limitation and an associated increase in soil C/N ratio induced a shift in the potential lifestyle of taxa from symbiotic to saprotrophic. Overall, water limitation appeared to alter soil microbial communities involved in nutrient cycling, pointing to potential consequences for forest health affected by prolonged episodes of drought.

Litter inputs exert greater influence over soil respiration and its temperature sensitivity than roots in a coniferous forest in north-south transition zone

The changes in carbon inputs of litter and roots to forest soils caused by climate change will result in a serious cascade effect on soil respiration and its temperature sensitivity (Q10). To differentiate and quantify the effects of surface litter and living roots on soil respiration and Q10, and further explore the role of abiotic factors and microbial properties on soil respiration and Q10, a short-term (two years) detritus input and removal treatment experiment was conducted in a coniferous forest of central China. Soil temperature, soil moisture, C/N, microbial biomass and community composition were analyzed to explore the drive mechanisms of soil respiration and Q10 in response to carbon inputs. The results showed that litter addition increased soil respiration by 22 %, while litter or roots removal did not affect soil respiration, which might be ascribed to the “priming effects” mediated by fresh plant litter. We also found that litter addition increased Q10, while litter removal decreased Q10. Litter addition significantly enhanced the microbial biomass for any single functional group and altered soil microbial community composition. Structural equation model further proved that microbial biomass and community composition exerted stronger impacts on Q10 than do soil abiotic factors. Soil moisture, microbial biomass and community structure were main factors in predicting soil respiration. The study highlights the important role of litter inputs compared with living roots in carbon cycling in short-term and deepens our understanding on the complex relationships among soil respiration, soil micro-environment and microbial community composition.

Inoculations of phosphate-solubilizing bacteria alter soil microbial community and improve phosphorus bioavailability for moso bamboo (Phyllostachys edulis) growth

Moso bamboo plantations suffer from phosphorus (P) limitations. A better understanding of soil P cycling contributes to the sustainable management and development of the bamboo forests. In this study, different phosphate-solubilizing bacteria (PSB) were applied to soils to stimulate bamboo growth, and the metagenomics method was employed to investigate the changes in soil microbial communities and relative abundances of functional genes. Meanwhile, soil properties and bamboo biomass and physiological indices were also quantitatively analyzed. The PSB inoculations changed soil P fractions and significantly elevated available P (AP) content by stimulating phosphatase activity and functional genes involved in P-transformation. The PSB inoculations significantly stimulated soil acid phosphatase activities and enhanced the relative abundances of functional genes associated with inorganic P-solubilization and organic P-mineralization. Moreover, increased soil available nutrients were beneficial to the moso bamboo growth, and the bamboo biomass in the different treatments increased by from 32.43 % to 69.04 % compared with the control treatment. Significant increases in root activity, carotenoid, chlorophyll a and total chlorophyll contents after the PSB inoculations also contributed to moso bamboo growth. The PSB strain inoculations shaped soil microbial communities and increased microbial connections. Besides adjusting soil P supplies and functional genes, the PSB also promoted the moso bamboo growth by increasing soil mineral N, AK and bamboo chlorophyll contents and stimulating functional microorganisms. Our study could provide a theoretical basis to improve soil nutrient utilization for moso bamboo with the PSB inoculations.

Nanoplastics alter ecosystem multifunctionality and may increase global warming potential.

Although the presence of nanoplastics in aquatic and terrestrial ecosystems has received increasing attention, little is known about its potential effect on ecosystem processes and functions. Here, we evaluated if differentially charged polystyrene (PS) nanoplastics (PS-NH2 and PS-SO3 H) exhibit distinct influences on microbial community structure, nitrogen removal processes (denitrification and anammox), emissions of greenhouse gases (CO2 , CH4 , and N2 O), and ecosystem multifunctionality in soils with and without earthworms through a 42-day microcosm experiment. Our results indicated that nanoplastics significantly altered soil microbial community structure and potential functions, with more pronounced effects for positively charged PS-NH2 than for negatively charged PS-SO3 H. Ecologically relevant concentration (3 g kg-1 ) of nanoplastics inhibited both soil denitrification and anammox rates, while environmentally realistic concentration (0.3 g kg-1 ) of nanoplastics decreased the denitrification rate and enhanced the anammox rate. The soil N2 O flux was always inhibited 6%-51% by both types of nanoplastics, whereas emissions of CO2 and CH4 were enhanced by nanoplastics in most cases. Significantly, although N2 O emissions were decreased by nanoplastics, the global warming potential of total greenhouse gases was increased 21%-75% by nanoplastics in soils without earthworms. Moreover, ecosystem multifunctionality was increased 4%-12% by 0.3 g kg-1 of nanoplastics but decreased 4%-11% by 3 g kg-1 of nanoplastics. Our findings provide the only evidence to date that the rapid increase in nanoplastics is altering not only ecosystem structure and processes but also ecosystem multifunctionality, and it may increase the emission of CO2 and CH4 and their global warming potential to some extent.

Changes in soil fertility and microbial communities following cultivation of native grassland in Horqin Sandy Land, China: a 60-year chronosequence

BackgroundGrassland conversion to cropland is a prevailing change of land use in traditionally nomadic areas, especially in the Mongolian Plateau. We investigated the effects of grassland conversion followed by continuous cultivation on soil properties and microbial community characteristics in Horqin Sandy Land, a typical agro-pastoral transition zone of Northern China. Soil samples were collected from the topsoil (upper 20 cm) across a 60-year cultivation chronosequence (5, 15, 25, 35 and 60 years) and unconverted native grassland. Soil physico-chemical properties were determined and high-throughput sequencing was used to assess microbial community diversity and composition.ResultsGrassland cultivation resulted in changes to soil properties in both the short and longer term. Initially, it significantly increased soil bulk density (BD), electrical conductivity (EC), soil total nitrogen (TN), available phosphorus (AP) and available potassium (AK) concentrations, while reducing soil water content (SWC) and soil organic carbon content (SOC). Over the next 35–55 years of continuous cultivation, the trend for most of these characteristics was of reversion towards values nearer to those of native grassland, except for SOC which remained highly depleted. Cultivation of grassland substantially altered soil microbial communities at phylum level but there was no significant difference in microbial α-diversity between native grassland and any cropland. However, soil bacterial and fungal community structures at phylum level in the croplands of all cultivation years were different from those in the native grasslands. Heatmaps further revealed that bacterial and fungal structures in cropland tended to become more similar to native grassland after 15 and 25 years of cultivation, respectively. Redundancy analysis indicated that SOC, EC and BD were primary determinants of microbial community composition and diversity.ConclusionsThese findings suggest that agricultural cultivation of grassland has considerable effects on soil fertility and microbial characteristics of Horqin Sandy Land. Intensive high-yield forage grass production is proposed as an alternative to avoid further native grassland reclamation, while meeting the grazing development needs in the ethnic minority settlements of eco-fragile regions.

Taxonomical and functional responses of microbial communities from forest soils of differing tree species diversity to drying-rewetting cycles

The predicted increases in drought in many forest ecosystems may alter soil microbial community diversity and activity, which may further depend on tree species richness. Shifts in microbial community composition and activity could engender changes in ecosystem function, notably, in soil greenhouse gas emissions and C storage. Using soils from mono-specific and mixed three-species forest stands from across Europe, we performed a microcosm experiment to test how soil microbial taxonomic and catabolic diversity are affected by repeated drying-rewetting (DRW) cycles and tree species mixing. We used Illumina sequencing and MicroResp™ analyses to explore community-level changes between microbial functional groups. DRW decreased bacterial richness and carbon substrate use diversity and increased fungal Shannon diversity. Additionally, microbial communities exposed to DRW changed their consumption of 11 out of 15 substrates significantly, suggesting microbial functional shifts. The legacy effect of tree species mixing influenced the structure of the microbial communities (i.e. taxonomic differential abundance) although, community weighted mean (CWM) values of absorptive root traits appeared to affect more strongly microbial richness, relative abundance, and Shannon diversity. No significant tree species mixing:DRW interaction was found for most microbial variables, except for the use of certain substrates and potentially differential abundance. Our data from a laboratory experiment with soils from different forest ecosystems underline that drought may cause shifts in microbial taxonomic and catabolic diversity, while tree species influences primarily taxonomic diversity through root traits.

Biostimulant Activity of Silicate Compounds and Antagonistic Bacteria on Physiological Growth Enhancement and Resistance of Banana to Fusarium Wilt Disease.

Biostimulants such as silicate (SiO32-) compounds and antagonistic bacteria can alter soil microbial communities and enhance plant resistance to the pathogens and Fusarium oxysporum f. sp. cubense (FOC), the causal agent of Fusarium wilt disease in bananas. A study was conducted to investigate the biostimulating effects of SiO32- compounds and antagonistic bacteria on plant growth and resistance of the banana to Fusarium wilt disease. Two separate experiments with a similar experimental setup were conducted at the University of Putra Malaysia (UPM), Selangor. Both experiments were arranged in a split-plot randomized complete block design (RCBD) with four replicates. SiO32- compounds were prepared at a constant concentration of 1%. Potassium silicate (K2SiO3) was applied on soil uninoculated with FOC, and sodium silicate (Na2SiO3) was applied to FOC-contaminated soil before integrating with antagonistic bacteria; without Bacillus spp. ((0B)-control), Bacillus subtilis (BS), and Bacillus thuringiensis (BT). Four levels of application volume of SiO32- compounds [0, 20, 40, 60 mL) were used. Results showed that the integration of SiO32- compounds with BS (108 CFU mL-1) enhanced the physiological growth performance of bananas. Soil application of 28.86 mL of K2SiO3 with BS enhanced the height of the pseudo-stem by 27.91 cm. Application of Na2SiO3 and BS significantly reduced the Fusarium wilt incidence in bananas by 56.25%. However, it was recommended that infected roots of bananas should be treated with 17.36 mL of Na2SiO3 with BS to stimulate better growth performance.

Chronic Warming and Nitrogen-Addition Alter Soil Organic Matter Molecular Composition Distinctly in Tandem Compared to Individual Stressors

Forest soils are major reservoirs of carbon (C), but these stores are threatened by increasing global temperatures and atmospheric nitrogen (N) deposition. These environmental stressors can alter soil microbial communities and soil organic matter (SOM) biogeochemistry through a variety of mechanisms. To investigate the impact of chronic warming, N-addition, and simultaneous warming and N-addition (warming + N) on forest soils, soil samples from the Harvard Forest Soil Warming and Nitrogen Addition (SWaN) experiment were analyzed after 14 years. Elemental analysis, targeted compound analysis by gas chromatography–mass spectrometry, and 13C nuclear magnetic resonance (NMR) spectroscopy were used to analyze changes in SOM in both the organic and mineral (0–10 cm) soil layers. Overall, changes in the molecular composition and microbial biomass were observed, but the extent of differences was unique to warming, N-addition, and warming + N treatments. Specifically, N-addition slowed SOM decomposition as measured via solid-state 13C NMR, while warming and warming + N accelerated SOM decomposition. Continued SOM decomposition after 14 years with warming + N signified a pronounced change to observations made after 4 and 10 years of experimental treatment. This is also demonstrative of how a two-factor approach leads to a unique molecular-level response that cannot be predicted from experiments with individual stressors alone. This study emphasizes the need to observe environmental stressors in tandem using a combination of molecular-level approaches to obtain a comprehensive understanding of how persistent anthropogenic activity will fundamentally alter forest soil systems.

Globally nitrogen addition alters soil microbial community structure, but has minor effects on soil microbial diversity and richness

Globally increasing nitrogen (N) deposition is recognized as an important regulator of soil microbial communities. However, how N enrichment affects soil microbial diversity, richness and community structure remains unclear at the global scale. Here, by focusing on high-throughput amplicon sequencing data from field experiments using N fertilizers only, we conducted a meta-analysis of a global dataset assessing the responses of microbial diversity (Shannon index), richness (Chao1, OTU richness) and community structure to N addition. Our results showed that N addition significantly reduced soil bacterial diversity (−2.3%), and such effect was significant in cropland (rather than grassland and forest) and with urea addition (rather than ammonium nitrate). However, there was no significant effect of N addition on soil fungal diversity and microbial (bacterial or fungal) richness. Moreover, N addition shifted microbial community structure likely due to the microbial adaptation to N-excess, but had no significant effect on microbial beta-diversity. Model-selection analysis further showed that the change in soil pH was the most important factor regulating the responses of soil bacterial diversity and richness to N addition. Overall, our results contribute to an in-depth understanding of the effects of N addition on soil microbial diversity and community structure in terrestrial ecosystems at the global scale.

Do full mechanized management strategies destroy soil health and fertility in sugarcane fields?

To provide new insights into whether soil health and fertility in realistic sugarcane production are destroyed by full mechanized cultivation (FMC), we investigated the differential structures and functions of soil bacterial and fungal communities by FMC and conventional artificial cultivation (CAC) treatments in sugarcane fields. The results showed that the soil water, total phosphorus, available nitrogen, phosphorus, and potassium contents significantly increased, but soil bulk density and pH significantly decreased in the FMC treatment compared with the CAC treatment. The activities of soil enzymes such as β-glucosidase, aminopeptidase, and acid phosphatase changed irregularly. Compared with the CAC treatment, significantly higher β-glucosidase activity and significantly lower aminopeptidase and acid phosphatase activities were detected in the FMC treatment. The soil microbial biomass carbon and microbial biomass phosphorus (MBP) increased; in particular, significant increases in MBP were observed in the FMC treatment. In contrast, soil microbial biomass nitrogen significantly decreased in the FMC treatment. In addition, mechanized cultivation altered soil microbial community structures and their metabolite profiles in sugarcane fields. Although soil bacterial diversity and abundance were significantly reduced, fungal abundance was not significantly different in the FMC treatment. Moreover, compared with CAC treatments, Actinobacteria, Proteobacteria, Firmicutes, Acidothermus, Chujaibacter, Conexibacter, and Longimycelium, were significantly enriched in the FMC treatments. In addition, fungal community composition, only Gymnopilus at the genus level was significantly enriched in the FMC treatment. Eight differential metabolites were detected in soils of sugarcane fields between the FMC and CAC treatments and were also found in background (BG) soil. Among them, only organic acids and sugars were positively or negatively correlated with the abundance of different bacteria. Starch and sucrose metabolism were the most differentially expressed metabolic pathways between the FMC and CAC treatments. These results suggest that FMC did not destroy soil health and fertility in sugarcane fields.

Functional substitutability of native herbivores by livestock for soil carbon stock is mediated by microbial decomposers.

Grazing by large mammalian herbivores impacts climate as it can favor the size and stability of a large carbon (C) pool in the soils of grazing ecosystems. As native herbivores in the world's grasslands, steppes, and savannas are progressively being displaced by livestock, it is important to ask whether livestock can emulate the functional roles of their native counterparts. While livestock and native herbivores can have remarkable similarity in their traits, they can differ greatly in their impacts on vegetation composition which can affect soil-C. It is uncertain how these similarities and differences impact soil-C via their influence on microbial decomposers. We test competing alternative hypotheses with a replicated, long-term, landscape-level, grazing-exclusion experiment to ask whether livestock in the Trans-Himalayan ecosystem of northern India can match decadal-scale (2005-2016) soil-C stocks under native herbivores. We evaluate multiple lines of evidence from 17 variables that influence soil-C (quantity and quality of C-input from plants, microbial biomass and metabolism, microbial community composition, eDNA, veterinary antibiotics in soil), and assess their inter-relationships. Livestock and native herbivores differed in their effects on several soil microbial processes. Microbial carbon use efficiency (CUE) was 19% lower in soils under livestock. Compared to native herbivores, areas used by livestock contained 1.5kg C m-2 less soil-C. Structural equation models showed that alongside the effects arising from plants, livestock alter soil microbial communities which is detrimental for CUE, and ultimately also for soil-C. Supporting evidence pointed toward a link between veterinary antibiotics used on livestock, microbial communities, and soil-C. Overcoming the challenges of sequestering antibiotics to minimize their potential impacts on climate, alongside microbial rewilding under livestock, may reconcile the conflicting demands from food-security and ecosystem services. Conservation of native herbivores and alternative management of livestock is crucial for soil-C stewardship to envision and achieve natural climate solutions.

Longer dry and wet spells alter the stochasticity of microbial community assembly in grassland soils

Climate change is increasing the duration of alternating wet and dry spells. These fluctuations affect soil water availability and other soil properties which are crucial drivers of soil microbial communities. While soil microbial communities have a moderate capacity to recover once a drought ceases, the expected alternation of strongly opposing regimes can challenge their capacity to adapt. Here, we set up experimental grassland mesocosms where precipitation frequency was adjusted along a gradient while holding total precipitation constant. The gradient varied the duration of wet and dry spells from 1 to 60 days during a total of 120 days, where we hypothesized that especially intermediate durations would increase the importance of stochastic community assembly due to frequent alternation of opposing environmental regimes. We examined bacterial and fungal community composition, diversity, co-occurrence patterns and assembly mechanisms across these different precipitation treatments. Our results show that 1) intermediate regimes of wet and dry spells increased the stochasticity of microbial community assembly whereas microbial communities at low and high regimes were subjected to more deterministic assembly, and 2) more persistent precipitation regimes (>6 days duration) reduced the fungal diversity and network connectivity but had little effect on bacterial communities. Collectively, these findings indicate that longer alternating wet and dry events lead to a less predictable and connected soil microbial community. This study provides new insight into the likely mechanisms through which precipitation persistence alters soil microbial communities and their predictability.