Phosphorus elevation erodes ectomycorrhizal community diversity and induces divergence of saprophytic community composition between vegetation types

Interguild fungal competition in litter and soil inversely modulate microbial necromass accumulation during Loess Plateau forest succession

Microbial interactions determine ecosystem carbon (C) and nutrient cycling, yet it remains unclear how interguild fungal interactions modulate microbial residue contribution to soil C pools (SOC) during forest succession. Here, we present a region-wide investigation of the relative dominance of saprophytic versus symbiotic fungi in litter and soil compartments, exploring their linkages to soil microbial residue pools and potential drivers along a chronosequence of secondary Chinese pine (Pinus tabulaeformis) forests on the Loess Plateau. Despite minor changes in C and nitrogen (N) stocks in the litter or soil layers across successional stages, we found significantly lower soil phosphorus (P) stocks, higher ratios of soil C: N, soil N: P and soil C: P but lower ratios of litter C: N and litter C: P in old (>75 years) than young stands (<30 years). Pine stand development altered the saprotroph: symbiotroph ratios of fungal communities to favor the soil symbiotrophs versus the litter saprotrophs. The dominance of saprotrophs in litter is positively related to microbial necromass contribution to SOC, which is negatively related to the dominance of symbiotrophs in soils. Antagonistic interguild fungal competition in litter and soil layers, in conjunction with increased fungal but decreased bacterial necromass contribution to SOC, jointly contribute to unchanged total necromass contribution to SOC with stand development. The saprotroph: symbiotroph ratios in litter and soil layers are mainly driven by soil P stocks and stand parameters (e.g., stand age and slope), respectively, while substrate stoichiometries primarily regulate microbial necromass accumulation and fungal: bacterial necromass ratios. These results provide novel insights into how microbial interactions at local spatial scales modulate temporal changes in SOC pools, with management implications for mitigating regional land degradation.

Tree species diversity increases soil microbial carbon use efficiency in a subtropical forest

Plant communities strongly influence soil microbial communities and, in turn, soil carbon (C) cycling. Microbial carbon use efficiency (CUE) is an important parameter for predicting soil C accumulation, yet how plant and soil microbial community traits influence microbial CUE remains poorly understood. Here, we determined how soil microbial CUE is influenced by plant and soil microbial community traits, by studying a natural gradient of plant species diversity in a subtropical forest. Our results showed that microbial CUE increased with increasing tree species diversity, suggesting a correlation between plant community traits and soil C storage. The specific soil properties that explained the greatest variation in microbial CUE were associated with microbial communities (biomass, enzyme activities and the ratio of oligotrophic to copiotrophic taxa); there were weaker correlations with plant-input properties, soil chemistry and soil organic C quality and its mineral protection. Overall, high microbial CUE was associated with soil properties correlated with increased tree species diversity: higher substrate availability (simple SOM chemical structures and weak mineral organic associations) and high microbial growth rates despite increased community dominance by oligotrophic strategists. Our results point to a mechanism by which increased tree species diversity may increase the forest C sink by affecting carbon use with the soil microbial community.

Co-responses of bacterial and fungal communities to fire management treatments in Mediterranean pyrophytic ecosystems

Cistus scrublands are pyrophytic ecosystems and occur widely across Mediterranean regions. Management of these scrublands is critical to prevent major disturbances, such as recurring wildfires. This is because management appears to compromise the synergies necessary for forest health and the provision of ecosystem services. Furthermore, it supports high microbial diversity, opening questions of how forest management practices impact belowground associated diversity as research related to this issue is scarce. This study aims to investigate the effects of different fire prevention treatments and site history on bacterial and fungi co-response and co-occurrence patterns over a fire-risky scrubland ecosystem. Two different site histories were studied by applying three different fire prevention treatments and samples were analyzed by amplification and sequencing of ITS2 and 16S rDNA for fungi and bacteria, respectively. The data revealed that site history, especially regarding fire occurrence, strongly influenced the microbial community. Young burnt areas tended to have a more homogeneous and lower microbial diversity, suggesting environmental filtering to a heat-resistant community. In comparison, young clearing history also showed a significant impact on the fungal community but not on the bacteria. Some bacteria genera were efficient predictors of fungal diversity and richness. For instance, Ktedonobacter and Desertibacter were a predictor of the presence of the edible mycorrhizal bolete Boletus edulis. These results demonstrate fungal and bacterial community co-response to fire prevention treatments and provide new tools for forecasting forest management impacts on microbial communities.

Soil microbiota associated with immune-mediated disease was influenced by heavy metal stress in roadside soils of Shanghai

Heavy metals (HMs) and total petroleum hydrocarbons (TPHs) in soils can be detrimental to both soil microorganisms and public health. However, the effects of HMs and TPHs on microbes as well as the consequent microbial-derived health risk remains unclear in soils by local roads where citizens are clearly accessible to traffic-derived pollutants. Herein, we sampled 84 roadside soils throughout Shanghai. We measured the levels of soil edaphic factors, 6 HMs, and alkane TPHs. We further focused on the responses of bacterial and fungal communities assessed via sequencing and network analysis. Results showed that all soil HMs exceeded background levels of Shanghai soil, while the levels of TPHs are comparable to unpolluted sites. Bacterial network nodes and links decreased sharply under HM stress whereas that of fungal networks remained unchanged. The differential pattern was attributed to the asynchronous response of key classes that fungal key classes were more resistant to HMs than bacteria. In addition, 66.8 % of fungal genera associated with immune-mediated disease increased with increased HM stress for its HM tolerance. Together our findings indicate that despite the relatively stable fungal community in response to environmental stresses, the elevation of harmful fungi likely pose threats to health of urban dwellers.

Altitudinal Variation Influences Soil Fungal Community Composition and Diversity in Alpine–Gorge Region on the Eastern Qinghai–Tibetan Plateau

Soil fungi play an integral and essential role in maintaining soil ecosystem functions. The understanding of altitude variations and their drivers of soil fungal community composition and diversity remains relatively unclear. Mountains provide an open, natural platform for studying how the soil fungal community responds to climatic variability at a short altitude distance. Using the Illumina MiSeq high-throughput sequencing technique, we examined soil fungal community composition and diversity among seven vegetation types (dry valley shrub, valley-mountain ecotone broadleaved mixed forest, subalpine broadleaved mixed forest, subalpine coniferous-broadleaved mixed forest, subalpine coniferous forest, alpine shrub meadow, alpine meadow) along a 2582 m altitude gradient in the alpine–gorge region on the eastern Qinghai–Tibetan Plateau. Ascomycota (47.72%), Basidiomycota (36.58%), and Mortierellomycota (12.14%) were the top three soil fungal dominant phyla in all samples. Soil fungal community composition differed significantly among the seven vegetation types along altitude gradients. The α-diversity of soil total fungi and symbiotic fungi had a distinct hollow pattern, while saprophytic fungi and pathogenic fungi showed no obvious pattern along altitude gradients. The β-diversity of soil total fungi, symbiotic fungi, saprophytic fungi, and pathogenic fungi was derived mainly from species turnover processes and exhibited a significant altitude distance-decay pattern. Soil properties explained 31.27−34.91% of variation in soil fungal (total and trophic modes) community composition along altitude gradients, and the effects of soil nutrients on fungal community composition varied by trophic modes. Soil pH was the main factor affecting α-diversity of soil fungi along altitude gradients. The β-diversity and turnover components of soil total fungi and saprophytic fungi were affected by soil properties and geographic distance, while those of symbiotic fungi and pathogenic fungi were affected only by soil properties. This study deepens our knowledge regarding altitude variations and their drivers of soil fungal community composition and diversity, and confirms that the effects of soil properties on soil fungal community composition and diversity vary by trophic modes along altitude gradients in the alpine–gorge region.

A Case Study Demonstrates That the Litter of the Rare Species Cinnamomum migao Composed of Different Tissues Can Affect the Chemical Properties and Microbial Community Diversity in Topsoil

The decomposition of litter plays an important role in the return of forest soil nutrients, as well as the growth and productivity of plants. With this study, we aimed to determine the impact of litter mulching on different tissues of Cinnamomum migao, a rare Chinese endemic species. In particular, seeds and pericarp are easily overlooked components of C. migao litter. In this study, we tested control (uncovered litter) and litter (leaf, branch, seed, and pericarp) mulching conditions and conducted a one-year litter decomposition experiment. The enzyme activities of urease enzyme (UE) and invertase enzyme (INV) were significantly improved by litter mulching. Catalase (CAT) enzyme activities in leaf, branch, and seed litter mulching were lower than in the control, whereas CAT activity in pericarp mulching was significantly higher than in the control. Although Mortierella, Cladophialophora, Acidothermus, Sphingomonas, and Burkholderia were the dominant microbes of topsoil in different mulching treatments, there were differences in the number and connectivity of microbial communities, and this change was correlated with soil organic carbon (SOC) and CAT enzyme activity. Compared with leaves and branches, seeds and pericarp as litter are also very important for nutrient return and affect topsoil microbes in C. migao forest, which may be of significance for the growth feedback of C. migao in biennial bearing.

Distribution and Assembly Processes of Soil Fungal Communities along an Altitudinal Gradient in Tibetan Plateau

In soil ecosystems, fungi exhibit diverse biodiversity and play an essential role in soil biogeochemical cycling. Fungal diversity and assembly processes across soil strata along altitudinal gradients are still unclear. In this study, we investigated the structure and abundance of soil fungal communities among soil strata and elevational gradients on the Tibetan Plateau using Illumina MiSeq sequencing of internal transcribed spacer1 (ITS1). The contribution of neutral and niche ecological processes were quantified using a neutral community model and a null model-based methodology. Our results showed that fungal gene abundance increased along altitudinal gradients, while decreasing across soil strata. Along with altitudinal gradients, fungal α-diversity (richness) decreased from surface to deeper soil layers, while β-diversity showed weak correlations with elevations. The neutral community model showed an excellent fit for neutral processes and the lowest migration rate (R² = 0.75). The null model showed that stochastic processes dominate in all samples (95.55%), dispersal limitations were dominated at the surface layer and decreased significantly with soil strata, while undominated processes (ecological drift) show a contrary trend. The log-normal model and the null model (βNTI) correlation analysis also neglect the role of niche-based processes. We conclude that stochastic dispersal limitations, together with ecological drifts, drive fungal communities.