Soil Fungal Community Composition Research Articles

Remediation of soils co-contaminated with cadmium and dichlorodiphenyltrichloroethanes by king grass associated with Piriformospora indica: Insights into the regulation of root excretion and reshaping of rhizosphere microbial community structure

Cadmium (Cd) and dichlorodiphenyltrichloroethane (DDT) are frequently detected in agricultural soils, which poses a threat to public health. This study investigated the effects of inoculation of king grass with Piriformospora indica on the remediation of soils co-contaminated with Cd and DDTs. After treatment for 90 days, the dry shoot and root biomass of king grass inoculated with P. indica markedly increased by 13.0–15.8% and 24.1–46.4%, respectively, compared with those of uninoculated plants. Inoculation with P. indica also increased the uptake of Cd and DDTs by shoots and roots of king grass. The removal efficiency of Cd and DDTs from soils reached 4.88–17.4% and 48.4–51.0%, respectively, in the presence of king grass inoculated with P. indica. Under three Cd–DDTs contamination conditions, root secretion of organic acids, alcohol, and polyamines was distinctively stimulated by P. indica inoculation of king grass compared with planting king grass alone. After phytoremediation, changes in soil bacterial and fungal community composition occurred at different contamination levels. Overall, the results showed that king grass associated with P. indica can be adopted for phytoextraction of Cd and DDTs from moderately contaminated soils by regulating root excretion and reshaping rhizosphere microbial community structure.

Reindeer grazing history determines the responses of subarctic soil fungal communities to warming and fertilization

Composition and functioning of arctic soil fungal communities may alter rapidly due to the ongoing trends of warmer temperatures, shifts in nutrient availability, and shrub encroachment. In addition, the communities may also be intrinsically shaped by heavy grazing, which may locally induce an ecosystem change that couples with increased soil temperature and nutrients and where shrub encroachment is less likely to occur than in lightly grazed conditions. We tested how 4yr of experimental warming and fertilization affected organic soil fungal communities in sites with decadal history of either heavy or light reindeer grazing using high-throughput sequencing of the internal transcribed spacer2 ribosomal DNA region. Grazing history largely overrode the impacts of short-term warming and fertilization in determining the composition of fungal communities. The less diverse fungal communities under light grazing showed more pronounced responses to experimental treatments when compared with the communities under heavy grazing. Yet, ordination approaches revealed distinct treatment responses under both grazing intensities. If grazing shifts the fungal communities in Arctic ecosystems to a different and more diverse state, this shift may dictate ecosystem responses to further abiotic changes. This indicates that the intensity of grazing cannot be left out when predicting future changes in fungi-driven processes in the tundra.

Dramatic shifts in fungal communities following application of hairy vetch (Vicia villosa Roth L.) in upland of Ultisol

The long-term high intensity continuous cropping with heavy application of mineral fertilization resulted in soil degradation and accumulation of soil-borne plant pathogens. Fungi are key microbial components and closely related to soil health in agroecosystem. In this study, the responses of fungal communities to different agricultural practices were investigated in upland of Ultisol using quantitative polymerase chain reaction (qPCR) and high-throughput sequencing (Illumina MiSeq). The study involved four management treatments: no fertilization (Control), mineral NPK fertilizer (NPK), NPK fertilizer plus peanut straw (NPKS), and NPK fertilizer plus planting green manure (i.e., hairy vetch; NPKG). By comparison with the NPK, application of NPKG significantly increased soil fertility and peanut yield. The NPKS and NPKG significantly increased soil fungal abundance relative to the NPK. Different agricultural practices significantly altered soil fungal community composition in Ultisol. Soil pH and phosphorus content were the two most pivotal drivers shaping fungal community structure. Compared to the NPK, the NPKS and NPKG significantly increased the relative abundance of Basidiomycota. The NPKG increased the relative abundance of certain plant-beneficial fungal taxa and decreased the relative abundance and diversity of plant-pathogen relative to NPK and NPKS, thereby contributing to suppressing continuous cropping barriers and increasing peanut productivity. Overall, our results suggested that planting hairy vetch might outperform NPK or returning peanut straw for improving peanut yield by increasing soil fertility and altering fungal community structure in upland of Ultisol.

Predictors of soil fungal biomass and community composition in temperate mountainous forests in Central Europe

Fungi are a highly diverse group of soil organisms greatly contributing to the functioning of forest ecosystems. Consequently, the understanding of factors affecting their productivity and distribution is needed for the understanding of litter and soil ecology. While several drivers of fungal community composition have been identified, it is less clear how their relative importance depends on topsoil habitats and how consistent it is across fungal ecological guilds. Moreover, the predictors of fungal biomass are much less known than those of the community composition. To fill these knowledge gaps, we collected and analyzed a comprehensive dataset from a Central European coniferous forest, covering a broad range of elevations and vegetation types and spanning from managed forests to protected forests with minimal human intervention. Fungal standing biomass and composition (including root, soil and litter habitats) was analyzed in relation to site characteristics, soil and litter chemistry and vegetation (intense botanical surveys and molecular analysis of plant roots). We found that fungal biomass and community composition in soil were vertically stratified in our study area. The nutrient-rich litter contained elevated fungal biomass content and it was dominated by saprotrophic fungi, whereas bulk soil, with less fungal biomass, was dominated by ECM fungi and relatively depleted of saprotrophs. We show that vegetation was a key predictor of fungal community composition across all ecological guilds of fungi and habitats. pH of soil or litter was a significant predictor of fungal community composition in all studied habitats, whereas climatic (altitude) effects were observed for fungal biomass and composition in bulk soil. Finally, P was the most important nutrient in our study, explaining >20% of variance in fungal biomass and affecting fungal community composition across habitats. Our results support the idea that intense atmospheric deposition of N during last decades may have shifted Central European forests from N-limitation to P-limitation. In light of increased global anthropogenic N inputs projected for the next century, our results suggest that fungal productivity might become P-limited rather than N-limited in temperate forests.

Effects of Simulated Warming on Soil Fungal Community Composition and Diversity

Effects of Simulated Warming on Soil Fungal Community Composition and Diversity

Response of Fungal Diversity, Community Composition, and Functions to Nutrients Management in Red Soil

Soil fungi play a critical role in plant performance and soil nutrient cycling. However, the understanding of soil fungal community composition and functions in response to different nutrients management practices in red soils remains largely unknown. Here, we investigated the responses of soil fungal communities and functions under conventional farmer fertilization practice (FFP) and different nutrient management practices, i.e., optimization of NPK fertilizer (O) with soil conditioner (O + C), with lime and mushroom residue (O + L + M), and with lime and magnesium fertilizer (O + L + Mg). Illumina high-throughput sequencing was used for fungal identification, while the functional groups were inferred with FUNGuild. Nutrient management practices significantly raised the soil pH to 4.79–5.31 compared with FFP (3.69), and soil pH had the most significant effect (0.989 ***) on fungal communities. Predominant phyla, including Ascomycota, Basidiomycota, and Mortierellomycota were identified in all treatments and accounted for 94% of all fungal communities. The alpha diversity indices significantly increased under nutrients management practices compared with FFP. Co-occurrence network analysis revealed the keystone fungal species in the red soil, i.e., Ascomycota (54.04%), Basidiomycota (7.58%), Rozellomycota (4.55%), and Chytridiomycota (4.04%). FUNGuild showed that the relative abundance of arbuscular mycorrhizal fungi and ectomycorrhizal fungi was higher, while pathogenic fungi were lower under nutrient management practices compared with FFP. Our findings have important implications for the understanding of improvement of acidic soils that could significantly improve the soil fungal diversity and functioning in acidic soils.

Fungal Community Composition and Diversity Vary With Soil Horizons in a Subtropical Forest.

Soil fungal communities, which drive many ecosystem processes, vary across soil horizons. However, how fungal communities are influenced by soil horizon layers remains largely unstudied. In this study, soil samples were collected from the organic horizon (O horizon) and mineral matter horizon (M horizon) in two sites of Dabie Mountain, China, and the effects of the two horizons on the soil fungal community composition were assessed based on Illumina MiSeq sequencing. Our results showed that soil fungal community composition varied with soil horizons, and soil fungal species richness and diversity in the O horizon were significantly higher than that in the M horizon. Total organic carbon (TOC), total organic nitrogen (TON), alkali-hydrolyzable nitrogen (AHN), available potassium (AK), and available phosphorus (AP) significantly influenced fungal community composition, abundance, and diversity across the two horizons (P < 0.05). Furthermore, precipitation was found to have a significant effect on fungal community composition. Our results demonstrate changes in fungal communities across soil horizons and highlight the importance of soil organic matter on fungal communities and diversity.

Altitude distribution of fungal community in Huoditang in Qinling Mountains, Northwest China.

Soil fungi play an important role in soil nutrient cycling and carbon storage in natural ecosystems. Dominant tree species showed altitude distribution in Huoditang forest in Qinling Mountains, whereas the corresponding changes of soil characteristics and microbial communities are still unclear. In this study, the variations of soil characteristics were investigated at five altitudes (1500, 1700, 1900, 2100 and 2300 m). The collected soil samples were sequenced by Illumina MiSeq sequencing platform, and the pattern of fungal community was studied. The results showed that soil available phosphorus concentration (AP) and soil pH increased significantly whereas soil moisture showed a downward trend with increasing altitude. The Shannon diversity index of soil fungi decreased and ACE richness index showed an opposite trend with increasing altitude. Basidiomycota (68.2%), Ascomycota (19.9%), and Mortierellomycota (1.7%) were dominant fungal phyla, which showed a 'U' shape or 'peak' pattern according to altitude. Agaricomycetes (64.2%), Sordariomycetes (5.8%), and Leotiomycetes (4.1%) were the dominant fungal classes. Results of redundancy analysis (RDA) showed that 89.1% of the total variations of soil fungal community were explained by soil characteristics, while AP, pH and altitude were the main driving factors for altitude variations of soil fungal communities. Soil characteristics had certain differences with altitude changes in Huoditang forest region in Qinling Mountains, which affected soil fungal community composition.

Abundant fungal and rare bacterial taxa jointly reveal soil nutrient cycling and multifunctionality in uneven-aged mixed plantations

Uneven-aged silvicultural practices can maintain habitat continuity and enhance biodiversity. Soil microorganisms play critical roles in multiple ecosystem functions (i.e., multifunctionality). However, little is currently known regarding the role of the microbial community in driving soil nutrient cycling and multifunctionality (SMF) in uneven-aged mixed plantations. In this study, we investigated soil bacterial and fungal community compositions and diversities, single-function related carbon (C), nitrogen (N), and phosphorus (P) cycling, and SMF indices in monoculture plantation (as a control) and three uneven-aged mixed plantation stands (4, 7, and 11 years old). Our results demonstrated that the soil C, N, P cycling, and SMF indices in uneven-aged mixed plantations increased by 17.9–55.2%, 20.0–54.0%, 0.7–21.6%, and 16.3–30.1% compared to monoculture plantation. The soil fungal alpha diversity (richness and Shannon diversity), nutrient cycling, and SMF significantly improved with stand age, but bacterial alpha diversity showed less variation. The beta diversities of bacteria and fungi showed notable variation with stand age and were predominantly affected by stand age and soil properties (soil organic C, total P, and C/N ratio), respectively. Additionally, the temporal turnover within the fungal community was higher than the turnover rates of the bacterial community. Soil fungal diversity and biomass were more sensitive to the stand structure change over a short period (11 years) than bacterial diversity and biomass. Furthermore, the fungal beta diversity and fungi/bacteria (F/B) ratio were strongly and positively correlated with nutrient cycling and SMF. Most importantly, the abundant fungal taxa (e.g., Mucoromycota and Mortierellomycota) were the major drivers of SMF, followed by rare bacterial taxa (e.g., Nitrospirae and Elusimicrobia). These findings indicate soil fungal and bacterial communities have different responses and undertake important roles in maintaining nutrient cycling and SMF when a monoculture plantation is converted into an uneven-aged mixed plantation.

Effects of plant community history, soil legacy and plant diversity on soil microbial communities

AbstractPlant and soil microbial diversities are linked through a range of interactions, including the exchange of carbon and nutrients but also herbivory and pathogenic effects. Over time, associations between plant communities and their soil microbiota may strengthen and become more specific, resulting in stronger associations between plant and soil microbial diversity.We tested this hypothesis at the end of a 4‐year field experiment in 48 plots with different plant species compositions established 13 years earlier in a biodiversity experiment in Jena, Germany. We factorially crossed plant community history (old vs. new plant communities) and soil legacy (old vs. new soil) with plant diversity (species richness levels 1, 2, 4 and 8, each with 12 different species compositions). We use the term ‘plant community history’ to refer to the co‐occurrence history of plants in different species compositions in the Jena Experiment. We determined soil bacterial and fungal community composition in terms of operational taxonomic units (OTUs) using 16S rRNA gene and ITS DNA sequencing.Plant community history (old plants) did not affect overall soil community composition but differentially affected bacterial richness and abundances of specific bacterial taxa in association with specific plant species compositions. Soil legacy (old soil) markedly increased soil bacterial richness and evenness and decreased fungal evenness. Soil fungal richness increased with plant species richness, regardless of plant community history or soil legacy, with the strongest difference between plant monocultures and mixtures. Specific plant species compositions and functional groups were associated with specific bacterial and fungal community compositions. Grasses increased fungal richness and evenness and legumes decreased fungal evenness, but bacterial diversity was not affected.Synthesis. Our findings indicate that as experimental ecosystems varying in plant diversity develop over time (2002–2010), plant species associate with specific soil microbial taxa. This can have long‐lasting effects on below‐ground community composition in re‐assembled plant communities, as reflected in strong soil legacy signals still visible after 4 years (2011–2015). Effects of plant community history on soil communities are subtle and may take longer to fully develop.

Response of Soil Fungal Diversity and Community Composition to Varying Levels of Bamboo Biochar in Red Soils.

Soil fungi play a vital role in soil nutrient dynamics, but knowledge of their diversity and community composition in response to biochar addition into red soil is either limited or inconsistent. Therefore, we determined the impact of bamboo biochar (BB) with increasing concentrations (0, 5, 20, and 80 g kg−1 of soil, referred to as B0, BB5, BB20, and BB80, respectively) on soil physicochemical properties and fungal communities (Illumina high-throughput sequencing) in red soil under Fokenia hodginsii (Fujian cypress). We found that increasing BB levels effectively raised the soil pH and soil nutrients, particularly under BB80. BB addition significantly increased the relative abundance of important genera, i.e., Basidiomycota, Mucoromycota, and Chytridiomycota that could play a key role in ecological functioning, e.g., wood degradation and litter decomposition, improvement in plant nutrients uptake, and resistance to several abiotic stress factors. Soil amended with BB exhibited a substantial ability to increase the fungal richness and diversity; BB80 > BB20 > BB5 > B0. Basidiomycota, Mucoromycota, Glomeromycota, Rozellomycota, Aphelidiomycota, Kickxellomycota, and Planctomycetes were positively associated with soil pH, total nitrogen, phosphorous, and carbon, and available potassium and phosphorous. Besides, the correlation analysis between the soil fungal communities and soil properties also showed that soil pH was the most influential factor in shaping the soil fungal communities in the red soil. These findings have significant implications for a comprehensive understanding of how to ameliorate acidic soils with BB addition, as well as for future research on sustainable forest management, which might increase soil fungi richness, diversity, and functionality in acidic soils.

Chemical composition controls the decomposition of organic amendments and influences the microbial community structure in agricultural soils

We assessed the soil carbon sequestration potential of various organic amendments of agricultural, municipal and industrial origin and the applicability of a soil carbon model to simulate it. The chemical composition of a large number of plant residues, manures, composts, digestates and biochars was determined and selected materials were incubated in soil to assess their decomposition rates and effects on soil microbial community structure. Decomposability was strongly correlated with the initial chemical composition determined by water, ethanol and acid extraction. Fresh plant materials decomposed the fastest, roots decomposed more slowly than aboveground biomass and processing decreased the decomposability of the materials. Soil carbon model Yasso07 predicted the decomposition of the amendments relatively well, except for fresh plant litter and fiber sludge from the pulp and paper industry which decomposed considerably faster than predicted by the model. Differences in the studied materials were also reflected in the soil microbial and fungal community composition. Plant root addition to laboratory microcosms induced a different soil microbial community compared to organic materials originating from the forest industry. Typical application rates of the studied amendments result in carbon sequestration at a rate sufficient to reach the goal of the 4/1000 initiative. The results can be used to select the most efficient measures to sequester carbon in croplands and to report the effects of practices like cover crop cultivation or organic matter addition.

Mycorrhizal type and soil pathogenic fungi mediate tree survival and density dependence in a temperate forest

The Janzen-Connell hypothesis has been explored by many ecologists in a great number of forests. Numerous studies have suggested that mycorrhizal type and fungal composition may affect the conspecific negative density dependence (CNDD) among tree species. However, how the variations and roles of mycorrhizal type and fungi compositions influence CNDD remains a challenge in temperate forests. We used tree demographic data in a 42–ha plot over ten years to test the effects of two types of tree mycorrhiza (arbuscular mycorrhiza: AM and ectomycorrhizal mycorrhiza: EM) on the survival of 45 species over three types of tree ontogeny (sapling, juvenile, adult trees), and the relationship between CNDD and soil fungal community composition of 8 common species. The results of this study show that AM tree species experienced stronger CNDD than EM tree species in each of the three ontogenetic stages. EM tree species with higher mutualistic fungi and lower pathogenic fungi may suffer lower CNDD. Individual trees with higher pathogenic fungi may be affected more severely by CNDD in our temperate forest. Our findings highlight the key roles of mycorrhizal association in mediating the strength of CNDD on tree survival, which may affect the plant community composition of temperate forests.

Impact of Dietary Protein Content on Soil Bacterial and Fungal Communities in a Rice-Crab Co-culture System.

Although co-culture of paddy fields with aquatic animals is lucrative, the ecological impacts of high-protein content entering the agricultural soil via animal pellet feed and feces have not been well studied. Moreover, the effects of dietary protein on soils and soil microbes remain unclear. To elucidate this, we examined soil bacterial and fungal community composition and temporal changes in paddy fields subjected to different protein-content diets via 16S/18S rRNA gene amplicon sequencing analysis with a high-throughput next-generation sequencer. MiSeq sequencing revealed that protein content significantly impacted fungal community structure. High-protein diets reduced bacterial community diversity and relative abundance in both July and October. The phylum-level bacterial taxonomic composition was not affected by diet treatment, while in fungi, a major phylum-level shift was evident. Hierarchically clustered analysis showed that high-protein diets significantly reduced the relative abundance of Brevundimonas in both July and October. Saprotrophic macrofungal diversity was negatively related to dietary protein content. Considering microbial community structure and environmental factors, ca. 15% protein content is appropriate for the rice-crab co-culture system that we studied.

Clary Sage Cultivation and Mycorrhizal Inoculation Influence the Rhizosphere Fungal Community of an Aged Trace-Element Polluted Soil.

Soil fungal communities play a central role in natural systems and agroecosystems. As such, they have attracted significant research interest. However, the fungal microbiota of aromatic plants, such as clary sage (Salvia sclarea L.), remain unexplored. This is especially the case in trace element (TE)-polluted conditions and within the framework of phytomanagement approaches. The presence of high concentrations of TEs in soils can negatively affect not only microbial diversity and community composition but also plant establishment and growth. Hence, the objective of this study is to investigate the soil fungal and arbuscular mycorrhizal fungi (AMF) community composition and their changes over time in TE-polluted soils in the vicinity of a former lead smelter and under the cultivation of clary sage. We used Illumina MiSeq amplicon sequencing to evaluate the effects of in situ clary sage cultivation over two successive years, combined or not with exogenous AMF inoculation, on the rhizospheric soil and root fungal communities. We obtained 1239 and 569 fungal amplicon sequence variants (ASV), respectively, in the rhizospheric soil and roots of S. sclarea under TE-polluted conditions. Remarkably, 69 AMF species were detected at our experimental site, belonging to 12 AMF genera. Furthermore, the inoculation treatment significantly shaped the fungal communities in soil and increased the number of AMF ASVs in clary sage roots. In addition, clary sage cultivation over successive years could be one of the explanatory parameters for the inter-annual variation in both fungal and AMF communities in the soil and root biotopes. Our data provide new insights on fungal and AMF communities in the rhizospheric soil and roots of an aromatic plant, clary sage, grown in TE-polluted agricultural soil.

Effects of Soil Properties and Plant Diversity on Soil Microbial Community Composition and Diversity during Secondary Succession

Soil microbial communities play an important role in maintaining the ecosystem during forest secondary succession. However, the underlying mechanisms that drive change in soil microbial community structures during secondary succession remain poorly defined in species-rich subtropical coniferous forests. In this study, Illumina high-throughput sequencing was used to analyze the variations in soil microbial community structures during forest secondary succession in subtropical coniferous forests in China. The role of soil properties and plant diversity in affecting soil bacterial and fungal communities was determined using random forest and structural equation models. Highly variable soil microbial diversity was observed in different stages of secondary succession. Bacterial community diversity rose from early to middle and late successional stages, whereas fungal community diversity increased from early to middle successional stages and then declined in the late stage. The relative abundance of Acidobacteria, Gemmatimonadetes, Eremiobacterota(WPS-2), Rokubacteria, and Mortierellomycota increased during succession, whereas the relative abundance of Ascomycota and Mucoromycota decreased. The community composition and diversity of the soil microbial community were remarkably influenced by plant diversity and soil properties. Notably, tree species richness (TSR) displayed a significant and direct correlation to the composition and diversity of both bacterial and fungal communities. The carbon-to-nitrogen (C:N) ratio had a direct impact on the bacterial community composition and diversity, and pH had a marked impact on the fungal community composition and diversity. Furthermore, succession stage and plant diversity indirectly impacted the composition and diversity of soil bacterial and fungal communities via soil properties. Overall, it can be concluded that soil intrinsic properties and plant diversity might jointly drive the changes in soil microbial community composition and diversity during secondary succession of subtropical coniferous forests.

Trichoderma asperellum alters fungal community composition in saline–alkaline soil maize rhizospheres

AbstractThe Songnen Plain is an important agricultural region in China with an abundance of saline–alkaline soil that significantly restricts maize growth. Trichoderma spp., free‐living fungi, are commonly used biofertilizers. The effects of Trichoderma asperellum on the fungal community in saline–alkaline soils remain unclear; hence, in this study, three T. asperellum conidium suspension concentrations were used: 0 g (control), 0.7 g (low dose), and 1.4 g (high dose) over three consecutive years, following which high‐throughput sequencing was conducted to analyze the effect of T. asperellum on fungal diversity in the rhizosphere soil. Changes in crop yield, soil salt ion content, and pH were also monitored. T. asperellum treatment effectively regulated the soil salt ion balance, lowered the pH, and improved the crop yield by 4.88–20.26%. Additionally, the T. asperellum treatment significantly increased the relative abundance of T. asperellum and Ceratobasidium sp and inhibited that of the pathogenic fungi Neonectria and Fusarium. Changes in the soil fungal community composition were closely associated with soil properties and yield. Our findings suggest that long‐term T. asperellum exposure can alleviate saline–alkaline stress for maize growth by decreasing soil pH and salt ion content and regulating the fungal microbial community, thereby increasing crop yield.

The short-term impacts of soil disturbance on soil microbial community in a degraded Leymus chinensis steppe, North China

The synergy between vegetation and soil is a fundamental driver of ecosystem restoration, yet the short-term impacts of soil disturbance on soil microbes and the relations between vegetation and soil during vegetation recovery remain unclear. We compared the responses of plants, soil physicochemical properties, and microbial communities after seven years of application of soil disturbance techniques (harrowing, HA; shallow ploughing, SP; and natural recovery, NR, the control) in a degraded Leymus chinensis steppe. Our results showed that bacterial community was more stable and did not change significantly under soil disturbance, but the fungal community was more sensitive to soil disturbance and was closely related to soil water content, bulk density, and relative aboveground biomass of dominant plant species. The results of this study suggest that soil disturbance techniques directly (mainly via changes in soil physical properties) and indirectly (mainly via changes in plant community composition) affected soil fungal community composition. Data show that SP largely facilitated the recovery of L. chinensis but decreased plant richness and diversity, resulted in a slower rate of soil microbial and soil quality restoration relative to the other treatments. It is also clear that HA and NR exerted positive effects on the recovery of the plant and soil microbial communities across degraded Leymus chinensis steppe over short timescales. Our results provide scientific guidance for more effective management of degraded grassland, and suggest that above- and belowground communities should be considered to be precise indicators of grassland ecosystem restoration. The long-term effects of soil disturbance techniques on soil microbial communities require further study.

Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage.

The climate-driven encroachment of shrubs into the Arctic is accompanied by shifts in soil fungal communities that could contribute to a net release of carbon from tundra soils. At the same time, arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these different vegetation types associate with contrasting fungal communities, the belowground consequences of climate change could vary among grazing regimes. Yet, at present, the impact of grazing on soil fungal communities and their links to soil carbon have remained speculative. Here we tested how soil fungal community composition, diversity and function depend on tree vicinity and long-term reindeer grazing regime and assessed how the fungal communities relate to organic soil carbon stocks in an alpine treeline ecotone in Northern Scandinavia. We determined soil carbon stocks and characterized soil fungal communities directly underneath and >3m away from mountain birches (Betula pubescens ssp. czerepanovii) in two adjacent 55-year-old grazing regimes with or without summer grazing by reindeer (Rangifer tarandus). We show that the area exposed to year-round grazing dominated by evergreen dwarf shrubs had higher soil C:N ratio, higher fungal abundance and lower fungal diversity compared with the area with only winter grazing and higher abundance of mountain birch. Although soil carbon stocks did not differ between the grazing regimes, stocks were positively associated with root-associated ascomycetes, typical to the year-round grazing regime, and negatively associated with free-living saprotrophs, typical to the winter grazing regime. These findings suggest that when grazers promote dominance of evergreen dwarf shrubs, they induce shifts in soil fungal communities that increase soil carbon sequestration in the long term. Thus, to predict climate-driven changes in soil carbon, grazer-induced shifts in vegetation and soil fungal communities need to be accounted for.

Nutrients available in the soil regulate the changes of soil microbial community alongside degradation of alpine meadows in the northeast of the Qinghai-Tibet Plateau

The alpine meadow in the Qinghai-Tibet Plateau has been seriously degraded due to human activities and climate change in recent decades. Understanding the changes of the soil microbial community in response to the degradation process helps reveal the mechanism underlying the degradation process of alpine meadows. We surveyed and analyzed changes of the vegetation, soil physicochemical properties, and soil microbial community in three degradation levels, namely, non-degradation (ND), moderate degradation (MD), and severe degradation (SD), of the alpine meadows in the northeastern Qinghai-Tibet Plateau. We found that as the level of degradation increased, plant cover, plant density (PD), above-ground biomass (AGB), plant Shannon-Wiener index (PS), soil water content (SWC), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) decreased significantly, while the soil pH increased from 7.20 to 8.57. Alpine meadow degradation significantly changed the composition of soil bacterial and fungal communities but had no significant impact on the diversity of the microbial communities. Functional predictions indicated that meadow degradation increased the relative abundances of aerobic_chemoheterotrophy, undefined_saprotroph, and plant_pathogen, likely increasing the risk of plant diseases. Redundancy analysis revealed that in ND, the soil microbial community was mainly regulated by PS, PH, PD, SWC, and soil pH. In MD, the soil microbial community was regulated by the soil's available nutrients and SOC. In SD, the soil microbial community was not only regulated by the soil's available nutrients but also influenced by plant characteristics. These results indicate that during alpine meadow degradation, while the changes in the plants and soil environmental factors both affect the composition of the soil microbial community, the influence of soil factors is greater. The soil's available nutrients are the main driving factors regulating the change in the soil microbial community's composition alongside degradation levels.