Microplastics are recognized as an emerging contaminant worldwide. Although microplastics have been shown to strongly affect organisms in aquatic environments, less is known about whether and how microplastics can affect different taxa within a soil community, and it is unclear whether these effects can cascade through soil food webs. By conducting a microplastic manipulation experiment, i.e. adding low-density polyethylene fragments in the field, we found that microplastic addition significantly affected the composition and abundance of microarthropod and nematode communities. Contrary to soil fauna, we found only small effects of microplastics on the biomass and structure of soil microbial communities. Nevertheless, structural equation modelling revealed that the effects of microplastics strongly cascade through the soil food webs, leading to the modification of microbial functioning with further potential consequences on soil carbon and nutrient cycling. Our results highlight that taking into account the effects of microplastics at different trophic levels is important to elucidate the mechanisms underlying the ecological impacts of microplastic pollution on soil functioning.

Allelopathy is an important process in plant communities. The effects of allelopathy on seed germination and seedling development have been extensively investigated. However, the influences of extract soaking time and concentration on the foregoing parameters are poorly understood. Here, we conducted a seed germination assay to determine the allelopathic effects of the donor herbs Achnatherum splendens (Trin.) Nevski, Artemisia frigida Willd., and Stellera chamaejasme L., from a degraded grassland ecosystem in northern China, on lettuce (Lactuca sativa L.) seed germination and early seedling growth. Extract soaking times (12 h or 24 h) did not exhibit significantly different effects on lettuce seed germination or seedling development. However, all aqueous herb extracts inhibited lettuce seed germination and root length (RI < 0) and promoted lettuce shoot length, stem length, leaf length, and leaf width (RI > 0) at both low (0.005 g mL⁻¹) and high (0.05 g mL⁻¹) concentrations. Moreover, A. splendens extracts increased seedling biomass (RI > 0) and synthetical allelopathic effect (SE > 0) at both concentrations. In contrast, both A. frigida and S. chamaejasme extracts had hormesis effects, which stimulate at low concentrations (RI > 0) but inhibit at high concentrations (RI < 0) on seedling biomass and synthetical allelopathic effect (SE). The results suggest that allelopathic potential may be an important mechanism driving the dominance of A. frigida and S. chamaejasme in degraded grasslands. Reseeding allelopathy-promoting species such as A. splendens may be beneficial to grassland restoration. The present study also demonstrated that seedling biomass, root and shoot length, and seed germination rate are the optimal bioindicators in allelopathy assays and could be more representative when they are combined with the results of multivariate analyses.

The conversion of grasslands to croplands is common in the agro-pastoral ecotone and brings potential risks to soil health and environmental safety. As the forming unit of soil structure, the status of soil aggregates determines soil health and is affected by multiple factors. This study investigated the changes in soil aggregate and main related factors in conversion grasslands with different managed years. Grassland conversion ages were selected as experimental treatments, which included unmanaged grassland, 3 years, 10 years, 30 years, and 50 years since grassland conversion. After grassland conversion, the proportion of large macro-aggregates with a particle size of >2 mm in the 0–10 cm soil layer decreased, small macro-aggregates with a particle size of 2–0.25 mm and micro-aggregates with a particle size of 0.25–0.053 mm increased, while aggregates with a particle size of <0.053 mm had no significant change. Soil chemical properties, most microorganisms and the soil aggregate stability indices MWD and GMD decreased at the early stage (<30 years) of the managed grasslands. After about 50 years of cultivation, soil chemical properties and microorganisms returned to equal or higher levels compared to unmanaged grasslands. However, the stability of aggregates (mean weight diameter (MWD) and geometric mean diameter (GMD)) did not recover to the initial state. MWD and GMD were positively correlated with most bacterial factors (total phospholipid fatty acids (PLFAs), bacteria, Gram-positive bacteria, Gram-negative bacteria, actinomycetes and arbuscular mycorrhizal fungi (AMF)) and some soil chemical properties (carbon, nitrogen and polysaccharides). According to the partial least square structural equation model, soil organic carbon, total nitrogen and phosphorus in the 0–10 cm soil layer explained 33.0% of the variance in MWD by influencing microorganisms. These results indicated that the stability of aggregates was directly driven by microorganisms and indirectly affected by soil organic carbon, total nitrogen and phosphorus.

The conversion of grassland to cropland alters the terrestrial carbon cycle. However, changes in soil organic carbon (SOC) induced by grassland reclamation are poorly quantified due to the scarcity of large‐scale‐sampling data. Through paired sampling of 101 cropland and 101 grassland plots, this study examined changes in SOC resulting from conversion of grassland to cropland in an agropastoral ecotone of northern China. Results showed that grassland reclamation caused an average decrease of 16.07% in the surface (0–10 cm) SOC content. Over 80% of this region experienced SOC loss, while less than 20% showed increased SOC. As grassland soil organic carbon increased, the sensitivity of soil organic carbon changes to climate change following grassland‐to‐cropland conversion decreased, while the positive effects of changes in water flux and the normalized difference vegetation index (NDVI) strengthened. The most important factor influencing the change in SOC after grassland reclamation was the change in NDVI in low and medium SOC grasslands and the change in vegetation transpiration in high‐SOC grasslands. This study found spatial heterogeneity in the effects of grassland reclamation on SOC at the regional scale and offers insights into enhancing regional SOC sequestration.

Understanding how litter diversity and soil fauna drive microbial communities is critical for revealing trophic cascades in decomposition processes. We conducted a 460‐day field decomposition experiment in a subtropical forest, placing litter mixtures of one to four tree species into mesh bags with 25 μm or 4 mm openings to create fauna‐excluded and fauna‐accessible treatments, and assessing microbial community composition and biomass using phospholipid fatty acid (PLFA) analysis. The results showed that the litter traits and diversity significantly influenced microbial PLFA content. Both fungal and bacterial PLFA content increased with higher levels of nitrogen, phosphorus, manganese, potassium, and leaf thickness in the mixed litter. Soil fauna had a significant impact on microbial PLFA content and its community distribution. A notable interaction between soil fauna and litter richness was observed: soil fauna slowed the decline of bacterial PLFA content as litter richness increased, highlighting their role in moderating the impact of litter diversity on microbial communities. Additionally, soil fauna reversed the relationship between mixed litter traits and arbuscular mycorrhizal fungi (AMF) PLFA content. While a negative correlation was observed in the absence of soil fauna, their presence turned it positive, demonstrating that soil fauna modifies the impact of litter traits on AMF. These findings demonstrate the intricate interactions between plant litter diversity, soil fauna, and microbes, highlighting the crucial role of soil fauna in modulating the effect of plant diversity on microbial communities during decomposition.

The stem base of alfalfa is a critical part for its overwintering, regeneration, and yield. To better understand the specificity and importance of the stem base, we analyzed the structure, metabolic substances, and transcriptome of the stem base using anatomical techniques, ultra-high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS), and RNA sequencing (RNA-seq), and compared it with stems and roots. The anatomical structure shows that the ratio of xylem to phloem changes at the base of the stem. A total of 801 compounds involved in 91 metabolic pathways were identified from the broadly targeted metabolome. Transcriptome analysis revealed 4974 differentially expressed genes (DEGs) at the stem base compared to the stem, and 5503 DEGs compared to the root. Comprehensive analyses of differentially accumulated compounds (DACs) and DEGs, in the stem base vs. stem, identified 10 valuable pathways, including plant hormone signal transduction, zeatin biosynthesis, α-Linolenic acid metabolism, histidine metabolism, carbon metabolism, carbon fixation in photosynthetic organisms, pentose phosphate pathway, galactose metabolism, and fructose and mannose metabolism. The pathways of plant hormone signal transduction and carbon metabolism were also identified by comparing the stem base with the roots. Taken together, the stem base of alfalfa is the transition region between the stem and root in morphology; in terms of material metabolism, its growth, development, and function are regulated through hormones and sugars.