● N fertilizer altered bacterial community compositions by changing soil nutrients.

Nitrogen (N) fertilization drives the structure and function of soil microbial communities, which are crucial for regulating soil biogeochemical cycling and maintaining ecosystem stability. Despite the N fertilizer effects on soil microbial composition and diversity have been widely investigated, it is generally overlooked that ecosystem processes are carried out via complex associations among microbiome members. Here, we examined the effects of five N fertilization levels (0, 135, 180, 225, and 360 kg N ha⁻¹) on microbial co-occurrence networks and key functional taxa such as ammonia-oxidizers in paddy soils. The results showed that N addition altered microbial community composition, which were positively related to soil total N and available phosphorus (P) contents. The abundance of ammonia-oxidizing archaea (AOA) significantly decreased after N addition, whereas ammonia-oxidizing bacteria (AOB) increased in N360 treatment. Compared with low-N group (N0 and N135), the high-N group (N225 and N360) shaped more complex microbial webs and thus improved the stability of the microbial community. Partial least squares path modeling further revealed that N fertilizer had a higher effect on microbial network complexity in the high-N group (0.83) than the low-N group (0.49). Although there were more positive links across all microbial networks, the proportion of negative links significantly increased in the high-N network, suggesting that excess N addition aggravated the competition among microbial species. Disentangling these interactions between microbial communities and N fertilization advances our understanding of biogeochemical processes in paddy soils and their effects on nutrient supply to rice production. Our findings highlighted that highly N-enriched paddy soils have more stable microbial networks and can better sustain soil ecological functions to cope with the ongoing environmental changes.

● Boreal and temperate forests had higher MNC and FNC/BNC than other forest biomes.

Soil microbial necromass carbon (MNC) is an important contributor to soil organic carbon (SOC) and plays a vital role in carbon sequestration and climate change mitigation. However, it remains unclear whether the content, contribution to SOC (MNC/SOC), and fungal-to-bacterial necromass carbon ratio (FNC/BNC) of MNC vary across forest biomes and types. By summarizing data from 1704 points across 93 forest sites, we explored the spatial patterns of MNC, MNC/SOC, and FNC/BNC in the surface layer of 0–20 cm of forest soils, as well as the controlling factors involved. Overall, boreal and temperate forests had higher MNC and FNC/BNC values than tropical, subtropical, and Mediterranean forests, whereas both boreal and Mediterranean forests had low MNC/SOC values. Mixed forests had higher MNC and lower FNC/BNC than broadleaved and coniferous forests, whereas MNC/SOC was higher in broad-leaved forests than that in coniferous forests. Interestingly, the dependence of MNC on forest type also varies among forest biomes. Regression analyses identified soil total N as one of the most important factors affecting MNC and MNC/SOC; whereas MAT, soil pH, and clay content were identified as the important factors affecting FNC/BNC. This synthesis is critical for managing soil MNC to mitigate climate change in forests.

● Metatranscriptomics uncovers the dynamic expression of functional genes in soil environments, providing insights into the intricate metabolic activities within microbial communities.

Metatranscriptomics is a cutting-edge technology for exploring the gene expression by, and functional activities of, the microbial community across diverse ecosystems at a given time, thereby shedding light on their metabolic responses to the prevailing environmental conditions. The double-RNA approach involves the simultaneous analysis of rRNA and mRNA, also termed structural and functional metatranscriptomics. By contrast, mRNA-centered metatranscriptomics is fully focused on elucidating community-wide gene expression profiles, but requires either deep sequencing or effective rRNA depletion. In this review, we critically assess the challenges associated with various experimental and bioinformatic strategies that can be applied in soil microbial ecology through the lens of functional metatranscriptomics. In particular, we demonstrate how recent methodological advancements in soil metatranscriptomics catalyze the development and expansion of emerging research fields, such as rhizobiomes, antibiotic resistomes, methanomes, and viromes. Our review provides a framework that will help to design advanced metatranscriptomic research in elucidating the functional roles and activities of microbiomes in soil ecosystems.

● Salt spray is a natural disturbance in coastal area of Southern China.

Salt spray is a natural disturbance in coastal region. Arbuscular mycorrhizal fungi (AMF) are recognized as bio-ameliorators of soil salinity in plants. However, the mechanism through which AMF protects Cinnamomum camphora against aerial salinity remains unclear. To address this knowledge gap, plants were subjected to four fungal regimes, namely sterilized fungal inoculum, Glomus tortuosum, Funneliformis mosseae, or a combination of these two fungi, and exposed to three sprayed-salt regimes (0, 7, or 14 mg NaCl cm⁻² d⁻¹) in a greenhouse. Salt spray significantly decreased photosynthetic capabilities, total dry weight, and salinity tolerance of non-mycorrhizal plants. Mycorrhizal inoculation, particularly a combination of G. tortuosum and F. mosseae, evidently mitigated the detrimental effects induced by salt spray. Meanwhile, mycorrhiza-mediated protection depended on the intensity of sprayed salt and the identity of fungal taxa. Furthermore, the enhanced resistance of mycorrhizal C. camphora seedlings to aerial salinity was mainly owing to increased leaf thickness and photosynthetic capabilities. These findings imply that inoculation with combined fungi could be an optimal strategy for cultivating C. camphora plants in coastal regions. The results gained hold the potential to offer both theoretical and practical guidance for the managers of coastal ecosystems in soil restoration and conservation.

● Changes in soil properties and microbial communities regulated rhizosphere protistan assemblages.

Understanding the responses of different rhizosphere microbial lineages to soil amendments during in situ remediation of Cd-contaminated soil is of great importance in the assessment of the restoration and crop health. Here, we evaluated the effects of lime (LM), biochar (BC), pig manure (PM), and a commercial Mg-Ca-Si conditioner (CMC) on the rice rhizosphere soil physicochemical properties and community assembly of bacteria, fungi, and protists in a six-year consecutive application of soil amendments field trial. Our results indicated that among the four amendments, the BC and CMC had the best efficiency in increasing soil pH, which were 5.2% and 16.2%, respectively. Despite the differences in soil Cd concentrations is not noticeable, all the soil amendment treatments significantly decreased the proportion of available Cd in total Cd compared to the control. Soil amendments significantly altered the diversity of bacterial community, while they had no effect on fungal and protistan communities. Linear discriminant analysis effect size (LEfSe) showed that the bacteria was more sensitive to soil amendment-induced changes. For protists, treatments with LM and BC changed the groups of protistan consumers, while treatments with PM and CMC significantly increased the relative abundances of protistan phototrophs. Co-occurrence network analysis revealed that soil amendments increased microbial network complexity and triggered the role of protists, especially for the predatory protists Cercozoa, on microbial trophic interactions. Further variation partitioning analysis revealed that edaphic properties, bacterial and fungal communities compositions together explained the 77% of the total variation in protistan community, and the stronger correlations between diversity of bacterial and protistan communities suggested that the bacteria community was a more important biotic driver of the protistan community. Overall, our findings demonstrate the distinct responses of rice rhizosphere microbial communities to soil amendment applications, highlighting the interactive associations between microbiomes, which is vital for enhancing our ability to develop effective strategies for sustainable soil management. This study enhances our understanding of the ecological roles of protists under soil amendment applications and highlights their potential contributions in bioremediation and environmental applications for Cd-contaminated soil.

● A new COX1 primer for soil nematode metabarcoding was designed, and this primer outperforms other commonly used COX1 primer pairs in species recovery and quantity of PCR products.

Microscopic nematodes play important roles in soil ecosystems and often serve as bioindicators of soil health. The identification of soil nematodes is often difficult due to their limited diagnostic characters and high phenotypic plasticity. DNA barcoding and metabarcoding techniques are promising but lack universal primers, especially for mitochondrial COX1 gene. In this study a degenerated COX1 forward primer COIFGED was developed. The primer pair (COIFGED/JB5GED) outperforms other four commonly used COX1 primer pairs in species recovery and quantity of polymerase chain reaction (PCR) products. In metabarcoding analysis, the reads obtained from the new primer pair had the highest sequencing saturation threshold and amplicon sequence variant (ASV) diversity in comparison to other COX1 as well as 18S rRNA primers. The annotation of ASVs suggested the new primer pair initially recovered 9 and 6 out of 25 genera from mock communities, respectively, outperformed other COX1 primers, but underperformed the widely used 18S NF1/18Sr2b primers (16 out of 25 genera). By supplementing the COX1 database with our reference sequences, we recovered an additional 6 mock community species bringing the tally closer to that obtained with 18S primers. In summary, our newly designed COX1 primers significantly improved species recovery and thus can be supplementary or alternative to the conventional 18S metabarcoding.

● The nitrogen (N) and phosphorus (P) addition promotes the abundance of soybean soil nematodes.

With global warming, the increasing of industrial and agricultural activities and demand for fossil fuels, large amounts of nitrogen and phosphorus compounds are released into the atmosphere, resulting in an annual increase in nitrogen and phosphorus deposition. The nematodes, as one of the main functional groups of soil organisms, occupy multiple trophic levels in soil detritus food networks. However, few studies on the effects of nitrogen and phosphorus on soil nematodes, and the results are uncertain. This experiment was conducted in soybean farmland and four treatments included control, nitrogen addition, phosphorus addition, and N + P addition. The results showed that both phosphorus and N + P addition significantly increased the abundance of soil nematodes, but that had no effects on soil nematodes richness. Redundancy analysis showed that nitrate nitrogen, soil moisture content, and pH were environmental factors driving different dietary changes in soil nematode communities. The effect of phosphorus addition on the abundance of nematode communities mainly affects ammonium nitrogen. Our findings revealed that nitrogen addition when phosphate fertilizer is added to soybean farmland will have a certain positive effect on the soil underground food web, which provides a basis for better explaining the effect of nitrogen and phosphorus addition on soybean farmland.

● Herbicide-based weeds control impacts wheat crops as well.

To address environmental concerns and manage resistant weeds, there is a growing demand for eco-friendly alternatives. In this study, we propose the integration of synthetic communities (SynComs) to reduce herbicide consumption. Four SynComs, consisting of bacteria isolated from weed or wheat rhizospheres, were first evaluated under greenhouse conditions. All SynComs enhanced wheat growth, which was manifested by increased Soil Plant Analysis Development (SPAD) values and fresh biomass. At the same time, SynCom C4 effectively reduced SPAD values and fresh biomass of the infesting weed, Phalaris minor, when combined with low-dose Axial herbicide. A field trial was then conducted using the C4 SynCom and various doses of Axial (100%, 75%, 50%, and 25%). Remarkably, the combination of C4 with 50% and 75% Axial significantly improved wheat growth by mitigating the side effects of herbicide on wheat. Weed infestation reduced grain yield by 16% and 25% at the dose of 50% and 75% Axial, respectively. The combination of Axial with C4 rescued up to 22% of grain yield loss under infested weed compared with Axial alone. Our findings suggested that the combination of herbicides with SynComs exhibited synergistic effects for controlling Phalaris minor and promoting wheat growth, so that such combination provides a sustainable and eco-friendly weed control strategy.

● Microbial attributes were compared between soil fauna gut and plant rhizosphere.

Diverse microbes inhabit animals and plants, helping their hosts perform multiple functions in agricultural ecosystems. However, the responses of soil fauna gut and plant rhizosphere microbiomes to livestock manure applications are still not well understood. Here we fed Protaetia brevitarsis larvae (PBL) with chicken manure and collected their frass. The frass and manure were applied as fertilizers to lettuce pots. We then compared the changes of microbial diversity, community assembly, and potential functions between the gut group (i.e., all PBL gut and frass samples) and the rhizosphere group (i.e., all rhizosphere soil samples). We revealed that manure applications (i.e., feeding or fertilization) decreased bacterial diversity in the gut group but increased that in the rhizosphere group. Particularly, the proportions of Bacilli in the gut group and Gammaproteobacteria in the rhizosphere group were increased (up to a maximum of 33.8% and 20.4%, respectively) after manure applications. Stochastic and deterministic processes dominated community assembly in the gut and rhizosphere microbiomes, respectively. Manure applications increased the microbial co-occurrence network complexity of both the gut and rhizosphere groups. Moreover, the proportions of functional taxa associated with human/animal pathogens in the gut group and carbon/nitrogen cycling in the rhizosphere group were enhanced (up to 2.6-fold and 24.6-fold, respectively). Our findings illustrate the different responses of microbial diversity, community assembly, and potential functions in soil fauna gut and plant rhizosphere to manure applications. The results could enhance our knowledge on the reasonable utilization of animal and plant microbiomes in agricultural management.

● ARB was investigated in different soil types following manure application.

Swine manure, commonly applied as organic compost in agricultural fields, is an important reservoir of antibiotic-resistant bacteria (ARB). Previous work indicated that manure application led to more antibiotic resistance genes in red soil compared with black soil and fluvo-aquic soil. Accordingly, the influencing mechanisms of soil types on the distribution of ARB was worthy of further exploration by a soil column experiment. The results showed that a higher shift in the operational taxonomic units and the community composition of chlortetracycline (CTC)-resistant bacteria (CRB) were observed in fluvo-aquic soil than in black and red soils. CTC induced antibiotic resistance development in soil indigenous microorganisms (Streptomyces, Pseudomonas, Bacillus, Rhodococcus, and Paenibacillus), and the induction was most obvious in fluvo-aquic soil. Streptomyces was significantly positively correlated with pH and organic matter. Additionally, LEfSe analysis indicated that the key different genera were Microbacteriaceae (black soil), Lactobacillus, unclassified_c__Bacilli and Paenibacillus (fluvo-aquic soil), and Dyella, Ralstonia and Bacillus (red soil). It was concluded that manure application led to higher CRB risk in fluvo-aquic soil compared with black and red soils. Overall, appropriate methods according to soil types are important ways to reduce the risk of soil resistant bacteria during manure return.

Plastic pollution is a growing concern in soil ecosystems worldwide. The accumulation of (micro)plastic debris leads to a unique microenvironment, termed the “plastisphere.” Notably, the dynamics and behaviors of the soil plastisphere diverge from its marine counterpart, where it is initially defined, thereby likely exhibiting an uncharacterized feature in ecological effects and biogeochemistry. The understanding of the soil plastisphere holds significant implications for environmental science and practical applications in pollution management and agricultural practices. Compared with the oceanic plastisphere, research on the soil plastisphere is still in its infancy with limited but significant studies contributing to current knowledge. A recent seminal work by Rillig et al. (Rillig et al., 2023. Nature Reviews Microbiology. doi:10.1038/s41579-023-00967-2) has inspired us and provided comprehensive insights into the characteristics and function of the soil plastisphere. In this commentary, we present core aspects of the soil plastisphere, encompassing its microbial communities, biogeochemical processes, and ecological implications, as well as highlight current methodologies probing this domain.

● Conservation tillage increases soil microarthropod abundance at the global scale.

Conservation tillage is crucial for preserving soil structure and fertility. However, the effects of no tillage on the abundance of soil microarthropods (Acari and Collembola) remain unclear, with contrasting results reported. To assess the global impact of no tillage, we compiled a data set consisting of 59 publications, from which we extracted 167 observations for microarthropod abundance, 193 observations for Acari abundance, and 176 observations for Collembola abundance. Our findings revealed significant increases in soil microarthropods (27.1%), Acari (22.1%), and Collembola (32.3%) compared to conventional tillage under no tillage. The impact varied with soil texture, precipitation, and soil nutrient availability. Furthermore, to assess the impact of reduced tillage, we extracted 46 observations for microarthropod abundance, 64 observations for Acari abundance, and 27 observations for Collembola abundance. Reduced tillage also showed positive effects, with a 28.4% increase in soil microarthropods and a 53.7% increase in Acari compared to conventional tillage. Our research demonstrates the beneficial effects of no tillage and reduced tillage on soil microarthropod abundance. However, the positive effect of conservation tillage on soil microarthropods differed in magnitude Collembola and Acari. Conservation tillage should be encouraged, particularly in regions with poor soil nutrients and high precipitation, to prevent further decline in soil microarthropod abundance.

● Pattern and mitigation potential of crop-specific fertilizer-N losses were assessed.

Understanding crop-specific fertilizer-nitrogen (N) loss patterns, driving factors, and mitigation potentials is vital for developing efficient mitigation strategies. However, analyses based on the gross magnitude of fertilizer-N losses within a growing season remain fragmented and inconclusive at a global scale. To address this gap, we conducted a global meta-analysis using 940 observations from 79 published ¹⁵N-tracing studies to assess the effects of natural factors, soil parameters, and N application rates on gross fertilizer-N losses in cereal-cropped soils. We found that China had the highest conventional fertilizer-N application and loss rates (230−255 and 75.9−114 kg N ha⁻¹ season⁻¹, respectively) and the lowest soil organic carbon (SOC) contents (10.6 g kg⁻¹) among the countries examined. Mean annual precipitation, SOC content, and soil pH were key parameters affecting fertilizer-N losses in wheat-, maize-, and rice-cropped soils, respectively. Fertilizer-N application rates were positively correlated with N loss amounts, while higher SOC levels led to lower losses. Adopting optimized N application rates combined with improving SOC levels could potentially mitigate 34.8%−59.6% of N losses without compromising crop yields compared with conventional practices. This study underscores the critical role of SOC in reducing N losses and suggests that future research should focus on innovative strategies and efficient organic amendments for enhanced SOC sequestration.

● Rhizosphere microbial network in crater had higher complexity than in volcanic cone.

Volcanic eruptions are significant natural disturbances that provide valuable opportunities to study their impacts on soil microorganisms. However, no previous studies have compared the rhizosphere microbial communities of Boehmeria nivea L. in volcanic craters and cones. To address this gap, we conducted a comprehensive investigation using Illumina MiSeq high-throughput sequencing to compare the rhizosphere microbial communities in volcanic craters and cones. Principal Coordinate Analysis revealed significant differences in the rhizosphere microbial communities between the crater and cone. The bacterial communities in the rhizosphere of the crater exhibited higher diversity and evenness compared to the cones. Moreover, the cones displayed more intricate bacterial networks than the crater (nodes 556 vs. 440). Conversely, fungal networks were more complex in the crater than the cone (nodes 943 vs. 967). Additionally, bacterial communities demonstrated greater stability than fungal ones within these volcanic soils (avgK 241.1 vs. 499.7) and (avgCC 1.047 vs. 1.092). Furthermore, the Structural Equation Model demonstrated a direct positive impact of alpha diversity on soil microbial community multifunctionality in the crater (λ = 0.920, P < 0.001). Our findings have presented the opportunity to investigate the characteristics of the rhizosphere microbial communities of Boehmeria nivea L. in the crater and cone.

● Comammox Nitrospira clade A and B showed contrasting responses to citrus planting.

Ammonia oxidizing bacteria (AOB), archaea (AOA), nitrite oxidizing bacteria (NOB) and complete ammonia oxidizers (comammox Nitrospira) are major players in nitrification. However, the distribution and community composition of these nitrifiers in intensively managed orchard soils are still unclear. Here, we chose soil samples from citrus orchards that had been planted for 5 years (5Y), 10 years (10Y), 20 years (20Y) and 30 years (30Y), and adjacent woodland (NF), to study the response of nitrifiers to long-term citrus plantation using quantitative PCR and MiSeq sequencing. Our results revealed that the ammonia and nitrite oxidation potentials in the 5Y soil were the highest, and decreased with increasing plantation age. The AOB abundance was higher in 5Y and 10Y soils than that in 20Y and 30Y soils. The abundance of comammox Nitrospira clade A increased with increasing plantation age, but comammox Nitrospira clade B showed the opposite tendency. MiSeq sequencing results indicated 54d9-like AOA and Nitrobacter-NOB were the dominant populations in 5Y and 10Y soils whereas Nitrososphaera-like AOA and Nitrospira-like NOB dominated in 20Y and 30Y soils. The conversion of woodland to orchard resulted in a significant shift of AOB population from Nitrosospira cluster 3a.1 to cluster 3a.2. In addition, soil pH and phosphorus (P) content were the major factors shaping nitrifying communities. This work suggested citrus plantation altered the distribution of community composition of nitrifiers by affecting soil chemical and physical conditions, and comammox Nitrospira could potentially play an important role in nitrification in intensive managed orchard soils.

● Soil aggregates affect soil respiration and its temperature sensitivity.

Understanding the dynamics of soil respiration, microbial carbon use efficiency (CUE), and temperature sensitivity (Q₁₀) in response to exogenous organic matter (EOM) input, soil aggregate size, and incubation temperature is crucial for predicting soil carbon cycling responses to environmental changes. In this study, these interactions were investigated by 180-day incubation of soil aggregates supplemented with EOM at various temperatures (5°C, 15°C and 25°C). The results reveal an ‘L-shaped’ trend in soil respiration on the time scale across all treatments, characterized by initial rapid declines followed by stability. EOM input and higher temperatures significantly enhance respiration rates. Notably, the respiratory rates of soil aggregates of different sizes exhibit distinct patterns based on the presence or absence of EOM. Under conditions without the addition of EOM, larger aggregates show relatively lower respiration rates. Conversely, in the presence of EOM, larger aggregates exhibit higher respiratory rates. Furthermore, Q₁₀ decreases with increasing aggregate size. The relationship between Q₁₀ and the substrate quality index (SQI) supports the carbon quality temperature (CQT) hypothesis, highlighting SQI’s influence on Q₁₀ values, particularly during later incubation stages. Microbial CUE decreases with EOM input and rising temperatures. Meanwhile, aggregate size plays a role in microbial CUE, with smaller aggregates exhibiting higher CUE due to enhanced nutrient availability. In conclusion, the intricate interplay of EOM input, aggregate size, and temperature significantly shapes soil respiration, microbial CUE, and Q₁₀. These findings underscore the complexity of these interactions and their importance in modeling soil carbon dynamics under changing environmental conditions.

● CH₄ emission rates followed an increased pattern during the growing season at Tibetan Plateau.

Microorganisms play pivotal roles in soil methane (CH₄) emissions and their functional genes are origins of a key mechanism for soil CH₄-cycling. However, understanding of the roles of specific genes (e.g., unique or shared genes carried by species) underlying CH₄-cycling remains elusive. Here, we measured CH₄ emission rates and investigated variations in microbial community and the abundance of genes carried by species during the growing season in alpine meadow on the Tibetan Plateau. We discovered that CH₄ emission rates increased from 394.4, 745.9, and 1092.7 µg CH₄ m⁻² h⁻¹, in April, June, and August, respectively, and had a positive correlation with unique genes carried by abundant species during the growing season. Moreover, we found that unique genes carried by abundant species involved in methanogenesis processes have a higher abundance than methanotrophic processes. Further analysis indicated that climate factors (i.e., mean monthly temperature (MMT) and mean monthly precipitation (MMP)) influenced microbial community and their functional genes, and therefore affected the CH₄ emission rates. Overall, the present study provides a novel insight into the variation of soil CH₄ emissions from a functional gene perspective, highlighting the important roles of unique genes carried by abundant species in CH₄ emissions in the Tibetan Plateau under seasonal variation.

● Cd alone or combined with microplastics (MPs) enhanced wheat biomass.

Microplastics and heavy metal contamination poses major threats to soil function and food security; however, their synergistic effects remain largely unclear. This study investigated the effects of single or combined addition of polyethylene (PE) microplastic (1% w/w) and cadmium (Cd; 1.5 and 5 mg kg^–1) on functional microbial communities in the wheat rhizosphere soil. We observed that the biomass of wheat increased by 142.44% under high doses of Cd addition. The bacterial alpha diversity in wheat bulk soil reduced by 37.34%–37.83% with the combined addition of microplastic and Cd. The addition of microplastic reduced the relative abundance of Proteus involved in nitrogen fixation by 19.93%, while the relative abundance of Proteus and Actinobacteria involved in nitrogen cycling increased with the increase of Cd concentration, increasing by 27.96%–37.37% and 51.14%–55.04%, respectively. FAPROTAX analysis revealed that increasing Cd concentration promoted the abundance of functional bacterial communities involved in nitrification/denitrification and nitrate/nitrite respiration in rhizosphere soil. A FunGuild analysis showed that the synergy of PE-microplastics and Cd increased the abundance of saprophytic fungi, suggesting an enhanced degradation function. Our findings provide new knowledge on the effects of microplastics and heavy metals on soil microorganisms and functional microbial communities in agricultural soil.

● Biocrusts are one of the most important components of the land cover in frozen ground regions on the Qinghai–Tibet Plateau, which increased the silt particle content, enhanced field moisture capacity, and reduced soil bulk density.

Biocrusts (BSCs) are widely distributed in frozen ground regions on the Qinghai-Tibet Plateau, and they are considered an important component of cold ecosystems. However, the specific impacts of BSCs on frozen soil remains relatively unclear. The aim of our study was to clarify the influence of BSCs (light BSCs and dark BSCs in two different succession stages) on the physical properties and ecological stoichiometry characteristics of frozen soil. Our results showed that BSCs increased the silt particle content in 20–40 cm soil layer, leading to a decrease in soil bulk density. And the field water capacity increased about 10%–40% compared to bare land. Additionally, BSCs significantly increased the contents of soil organic carbon (SOC, 22.6–30.8 g kg⁻¹) and total nitrogen (TN, 2.1–2.8 g kg⁻¹) in the upper 40 cm soil layer, both of them were approximately 1.3–2.0 and 1.3–4.0 times higher than those observed in bare land. However, BSCs did not have significant influence on soil total phosphorus (TP). BSCs had a significant impact on the stoichiometric ratios within 40 cm. The C/N ratios of the two types of BSCs ranged from 8.8 to 13.5, the C/P ratios ranged from 6.6 to 13.8, and the N/P ratios ranged from 0.6 to 1.2, which were all higher than those of the bare land. There were no significant differences among the C/N, C/P, and N/P ratios between two types of BSCs. However, the increment of C/P and N/P ratios of dark BSCs were significantly higher than those of light BSCs within 0–30 cm, which indicated that a reduction in the availability of phosphorus during the later stages of BSCs succession. These findings provided a theoretical basis for further research on the ecological functions of BSCs in frozen ground regions.

● Fungi outperformed bacterial in maintaining the microbial co-occurrence networks.

The interplay between soil micro-organisms in mountain ecosystems critically influences soil biogeochemical cycles and ecosystem processes. However, factors affecting the co-occurrence patterns of soil microbial communities remain unclear. In an attempt to understand how these patterns shift with elevation and identify the key explanatory factors underpinning these changes, we studied soil bacterial and fungal co-occurrence networks on Mt. Seorak, Republic of Korea. Amplicon sequencing was used to target the 16S rRNA gene and ITS2 region for bacteria and fungi, respectively. In contrast to bacteria, we found that fungi were predominantly situated in the core positions of the network, with significantly weakened co-occurrence with increasing elevation. The different co-occurrence patterns of fungal and bacterial communities could be resulted from their distinct responses to various environments. Both abiotic and biotic factors contributed significantly to shaping co-occurrence networks of bacterial and fungal communities. Fungal richness, bacterial community composition (indicated by PCoA1), and soil pH were the predominant factors influencing the variation in the entire microbial co-occurrence network. Biotic factors, such as the composition and diversity of bacterial communities, significantly influenced bacterial co-occurrence networks. External biotic and abiotic factors, including climatic and vegetative conditions, had a significant influence on fungal co-occurrence networks. These findings enhance our understanding of soil microbiota co-occurrences and deepen our knowledge of soil microbiota responses to climatic changes across elevational gradients in mountain ecosystems.