Cover crops are increasingly recognized for their role in enhancing the multifunctionality and health of soil. Previous studies have focused largely on the effects of cover crop residues and have overlooked the impacts of living cover crops on the soil biochemical processes and nutrient cycling. The aim of this study is to bridge this gap by examining the effects of different types of living cover crops, such as legumes, grass, and their mixtures, on the soil nutrients and microbial communities. We conducted a field experiment in northeastern China using an Alfisol and intercropped cover crops with maize. During the growing season, we characterized microbial biomass and community structure using phospholipid fatty acid (PLFA) analysis and assessed microbial activity through enzyme activities related to carbon (C), nitrogen (N) and phosphorus (P). Additionally, we employed the enzyme vector model to evaluate potential microbial metabolic limitations. Compared with the control plots without cover crops, the legume treatment significantly increased dissolved organic carbon (DOC) and available nitrogen, particularly altering the microbial community structure during the maize growth stages. This change shifted the microbial functional group ratios towards enhanced C acquisition by soil microbes, indicating alleviated microbial C limitation in legume treatment. In contrast, the grass treatment maintained the soil organic carbon (SOC) and total nitrogen (TN) levels, and increased the total microbial biomass at the later growth stage. Compared with those in the other treatments, the biomass of bacterial groups in the grass treatment was more responsive, and the activities of the C, N and P enzymes were higher. Furthermore, the mixture treatment merged the benefits of both the legume and grass cover crops, enhancing both DOC and available N contents and maintaining SOC and TN levels. The mixture treatment significantly affected the microbial community structure without altering microbial nutrient limitations. Thus, the mixture treatment is recommended for application in cover crop-maize intercropping systems. In conclusion, our study captured the temporal dynamic shifts in the microbial functional groups associated with different microbial life strategies from intercropping different types of living cover crops with maize. This research refines our understanding of the role of cover crops in supporting belowground ecosystems and highlights the importance of living mulch in sustainable agricultural management.

Organic inputs from aboveground litter and underground roots are an important factor affecting nutrient cycling in forest ecosystems. However, we still know little about the seasonal effects of the interaction between aboveground and underground organic inputs on soil organic carbon, nutrients and microorganisms after vegetation restoration in degraded red soil. Therefore, we focused on a mixed forest dominated by Schima superba and Pinus massoniana that had been restored for 27 years on eroded and degraded red soil in a subtropical region. Five treatments were set as follows: retaining aboveground litter + retaining root + retaining mycorrhizae (LRM, control treatment), doubling aboveground litter + retaining root + retaining mycorrhizae (DLRM), removing aboveground litter + retaining root + retaining mycorrhizae (NRM), removing aboveground litter + removing root + retaining mycorrhizae (NNM), and removing aboveground litter + removing root + removing mycorrhizae (NNN). After more than three years of treatment, DLRM, NRM, NNM, and NNN treatments reduced soil moisture content by 32.0-56.8 % in the rainy season compared with the LRM treatment. Soil total nitrogen and ammonium nitrogen concentrations were the highest in the DLRM treatment. Soil ammonium concentration and pH were higher in the rainy season than those in the dry season, while soil nitrate concentration was higher in the dry season. Soil available phosphorus concentration in the dry season decreased by 64.5 % in the DLRM treatment, while they were 2.0-10.7 times of those in the LRM, NRM, NNM, and NNN treatments compared to the rainy season. Soil microbial communities were dominated by bacteria across treatments, accounting for 74.0-75.5 % of the total phospholipid fatty acid (PLFA) of soil microbes, and there was no significant difference among treatments. Except for fungi, the total PLFAs of soil microorganisms and the PLFA content of each microbial taxon were higher in the dry season than those in the rainy season. The F/B value in the rainy season was higher than that in the dry season. The PLFA contents of gram-positive bacteria and actinomyces in the DLRM and NRM treatments were higher than those in the NNM treatment, and PLFA contents of both in the dry season were 1.5 and 1.6 times of those in the rainy season, respectively. Soil total phosphorus and pH had the highest contribution to soil microbial community changes in rainy and dry seasons, respectively. Comprehensive evaluation showed that double aboveground litter addition was more conducive to soil quality improvement. In conclusion, litter, roots and mycorrhiza manipulations affected the PLFA contents of soil microorganisms through the regulation of soil physicochemical properties, rather than the proportions of each microbial taxon in the total PLFAs, which was related to the season. The results can provide a theoretical basis for soil quality improvement as driven by soil microorganisms during the restoration of degraded red soil.

The frequency of forest fires has increased dramatically due to climate change. The occurrence of forest fires affects the carbon and nitrogen cycles and react to climate change to form a positive feedback mechanism. These effects further impact the distribution of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) and the soil microbial community structure. In addition, permafrost degradation can significantly affect the microorganisms in the soil. Based on these findings, this review examines the effects of fire intensity and post-fire recovery time on permafrost, the soil microbial community, MBC, MBN, and their interrelationships. This review demonstrated that (1) fires alter the condition of surface vegetation, reduce the organic layer thickness, redistribute snow, accelerate permafrost degradation, and even lead to permanent changes, where the restoration of the pre-fire state would require several decades or even centuries; (2) soil microbial community structure, soil MBC, and MBN negatively correlate with fire intensity, and the effects become more pronounced with increasing fire intensity; and (3) the structural diversity and stability of the soil microbial community were improved with time, and the amount of MBC and MBN increases as the years after a fire go by; it would still take more than ten years to recover to the pre-fire level. However, the relationship between permafrost degradation and soil microbes after forest fires is still unclear due to a lack of quantitative research on the mechanisms underlying the changes in soil microorganisms resulting from fire-induced permafrost degradation. Therefore, expanding quantitative studies and analyses of the mechanisms of interactions between forest fires, permafrost, and soil microorganisms can provide a scientific basis for understanding ecosystem carbon pools and dual-carbon targets in Arctic-boreal permafrost regions.

PurposeStripping topsoil and transplanting seedlings damage the plough layer, reduce soil quality, and hinder food production. It is therefore urgent to rapidly improve the fertility of such plough layer damaged soils; however, there is a lack of available materials, quality evaluation methods, and application techniques.Materials and methodsUsing moss peat (M), rice husk biochar (R), sawdust biochar (S), vegetable corn husk (C), and microbial inoculants as raw materials, a novel carbon-rich soil improvement materials (CRSIM) were created.Results and discussionThe results showed that when M and R are mixed at mass ratios of 1:1, 2:1, and 3:1, M and S are mixed at a mass ratio of 3:1, mixing with C at a mass ratio of 10:1, and adding microbial inoculant Bacillus subtilis, the high-quality CRSIM can be formed ((M + R)10C1, (2 M + R)10C1, (3 M + R)10C1, and (3 M + S)10C1)), which showed loose texture, high organic matter, and stability. Adding the above four CRSIM to plough layer damaged soil at the ratio of 1 to 8% can significantly reduce the soil bulk density, increase SOC and MBC content and carbon cycling enzyme activity, and change SOC chemical composition. Among them, the most beneficial material was (3 M + R)10C1, which increased wheat yield 5.6 times compared to CK when applied to the soil. In addition, CRSIM significantly influenced bacterial community composition and diversity more than fungi. They had greater strength in microbial carbon sequestration strategies while reducing soil microbial respiration intensity and qCO2, suggesting that these CRSIM favor the development of microbiota that contributes to soil C storage.ConclusionsIn summary, mixing peat and biochar can create a novel CRSIM for plough layer damaged soil, which can improve soil quality and increase soil carbon sequestration.

Understanding how soil microbes respond to permafrost thaw is critical to predicting the implications of climate change for soil processes. However, our knowledge of microbial responses to warming is mainly based on laboratory thaw experiments, and field sampling in warmer months when sites are more accessible. In this study, we sampled a depth profile through seasonally thawed active layer and permafrost in the Imnavait Creek Watershed, Alaska, USA over the growing season from summer to late fall. Amplicon sequencing showed that bacterial and fungal communities differed in composition across both sampling depths and sampling months. Surface communities were most variable while those from the deepest samples, which remained frozen throughout our sampling period, showed little to no variation over time. However, community variation was not explained by trace metal concentrations, soil nutrient content, pH, or soil condition (frozen/thawed), except insofar as those measurements were correlated with depth. Our results highlight the importance of collecting samples at multiple times throughout the year to capture temporal variation, and suggest that data from across the annual freeze-thaw cycle might help predict microbial responses to permafrost thaw.

Permafrost degradation may induce soil carbon (C) loss, critical for global C cycling, and be mediated by microbes. Despite larger C stored within the active layer of permafrost regions, which are more affected by warming, and the critical roles of Qinghai-Tibet Plateau in C cycling, most previous studies focused on the permafrost layer and in high-latitude areas. We demonstrate in situ that permafrost degradation alters the diversity and potentially decreases the stability of active layer microbial communities. These changes are associated with soil C loss and potentially a positive C feedback. This study provides insights into microbial-mediated mechanisms responsible for C loss within the active layer in degraded permafrost, aiding in the modeling of C emission under future scenarios.