● Response of growth rate and antioxidative system of ten Bacillus strains to acid stresses was assayed.

Environmental changes including soil acidification exert obvious stresses on soil ecosystems and influence soil microorganisms. In this study, ten microbial strains were incubated under different acid treatments to investigate responses of microbial growth and antioxidative system to acid stress. All the strains belong to Bacillus genus, but exhibit distinct ecological functions. We observed that these microbial strains had obviously different pH tolerance threshold, in spite of the close phylogenetic classification among strains. Acid stresses exerted significant effects on microbial antioxidative system, including superoxide dismutase (SOD), catalase (CAT) and glutathione transferring enzymes (GPX and GR) and reactants (GSH and GSSH), but the effects were strain specific. Furthermore, we found acid stress effects on total variances of the investigated microbial antioxidative system along the first two principal components (PCs). Activities of CAT and SOD contributed substantially to PC1 that reflected obvious acid effects on NC7 and ZC4, and closely related to intracellular malondialdehyde content. The GSSG activities and GSH/GSSG contributed greatly to PC2 that unveiled acid stress effects on most of the microbial strains. Our results highlight substantially heterogeneous responses of microbial strains to acid stress and support that phylogenetic closeness does not imply functional similarity of soil microorganisms under environmental changes.

● LDPE had no effect on the mortality, growth, and reproduction of earthworms.

Cadmium (Cd) can accumulate in the food chain, with serious impacts on human health and safety. Microplastics (MPs) such as low-density polyethylene (LDPE) should be considered not only as a single pollutant but also as a carrier of other pollutants. In this study, we investigated the joint effects of 30% LDPE and 313 mg kg⁻¹ Cd on mortality, growth, reproduction, microstructure, DNA damage, oxidative stress, and mRNA levels in the earthworm Eisenia fetida. We found that 313 mg kg⁻¹ Cd inhibited growth and reproduction and damaged the microstructures of the skin and intestine. Meanwhile, LDPE had no effect on the mortality, growth, or cocoon production of earthworms. Moreover, it did not increase the mortality, growth, or inhibition of cocoon production caused by Cd and instead alleviated the DNA damage in coelomocytes caused by Cd treatment. Finally, it did not alter the accumulation of Cd in the worms. These indicators can be used for toxicity safety assessment and soil ecological risk assessment of LDPE and Cd cooccurrence in soil.

● Bacterial richness declined but fungal richness increased under salinization.

Soil salinization is a typical environmental challenge in arid regions worldwide. Salinity stress increases plant convergent adaptations and facilitative interactions and thus destabilizes communities. Soil bacteria and fungi have smaller body mass than plants and are often efficient against soil salinization, but how the stability of bacterial and fungal communities change with a wide range of soil salinity gradient remains unclear. Here, we assessed the interactions within both bacterial and fungal communities along a soil salinity gradient in the Taklamakan desert to examine (i) whether the stability of bacterial and fungal communities decreased with soil salinity, and (ii) the stability of which community decreased more with soil salinity, bacteria or fungi. Our results showed that the species richness of soil fungi increased but that of soil bacteria decreased with increasing salinity in topsoils. Fungal communities became more stable under soil salinization, with increasing compartmentalization (i.e., modularity) and proportion of competitions (i.e., negative:positive cohesion) as salinity increased. Bacterial communities exhibited no changes in modularity with increasing salinity and smaller increases in negative:positive cohesion under soil salinization compared to fungal communities. Our results suggest that, by altering interspecific interactions, soil salinization increases the stability of fungal not bacterial communities in extreme environments.

● Reduced oxygen increased microbial metabolic quotient (qCO₂).

Mangroves are one of the most ecologically sensitive ecosystems to global climate change, which have cascading impacts on soil carbon (C), nitrogen (N) and phosphorus (P) cycling. Moreover, mangroves are experiencing increasing N and P loadings and reduced oxygen availability due to intensified climate change and human activities. However, both direct and interactive effects of these perturbations on microbially mediated soil C, N and P cycling are poorly understood. Here, we simultaneously investigated the effects of N and P loadings and reduced oxygen on microbial biomass, microbial respiration, and extracellular enzyme activities (EEAs) in mangrove soils. We calculated the microbial metabolic quotient (qCO₂), which is regarded as a useful inverse metric of microbial C use efficiency (CUE). Our results show that reduced oxygen significantly increases both qCO₂ and microbial specific EEAs (enzyme activity per unit of microbial biomass) for C-, N- and P-acquisition regardless of N or P loadings. Furthermore, we found that qCO₂ positively correlated with microbial specific EEAs under reduced oxygen, whereas no clear relationship was detected under ambient oxygen. These results suggest that reduced oxygen increases microbial specific EEAs at the expense of increasing microbial respiration per unit biomass, indicating higher energy cost per unit enzyme production.

● Fertilization had stronger impact on the root microbiome than on the soil microbiome.

Plant health and performance are highly dependent on the root microbiome. The impact of agricultural management on the soil microbiome has been studied extensively. However, a comprehensive understanding of how soil types and fertilization regimes affect both soil and root microbiome is still lacking, such as how fertilization regimes affect the root microbiomeʼs stability, and whether it follows the same patterns as the soil microbiome. In this study, we carried out a long-term experiment to see how different soil types, plant varieties, and fertilizer regimens affected the soil and root bacterial communities. Our results revealed higher stability of microbial networks under combined organic-inorganic fertilization than those relied solely on inorganic or organic fertilization. The root microbiome variation was predominantly caused by total nitrogen, while the soil microbiome variation was primarily caused by pH and soil organic matter. Bacteroidetes and Firmicutes were major drivers when the soil was amended with organic fertilizer, but Actinobacteria was found to be enriched in the soil when the soil was treated with inorganic fertilizer. Our findings demonstrate how the soil and root microbiome respond to diverse fertilizing regimes, and hence contribute to a better understanding of smart fertilizer as a strategy for sustainable agriculture.

• Soil macrofaunal biomass varied in a nonlinear pattern during degradation.

The alpine wetlands in the Qinghai-Tibetan Plateau have degraded in recent decades. However, the response of the soil food web to the degradation is still unclear. Four habitats including a wet meadow (WM), a grassland meadow (GM), a moderately degraded meadow (MDM) and a severely degraded meadow (SDM) (sandy meadows) were selected along the degrees of degradation. The soil macrofaunal biomass and the environmental factors of vegetation and soil were investigated. The soil macrofaunal community biomass increased significantly from WM to MDM and decreased to a very small amount in SDM, with most taxa disappearing. The biomass of the trophic groups of detritivores, herbivores and predators exhibited similar responses to soil macrofaunal communities. The relative biomass of detritivores increased from WM to MDM, but herbivores responded in an opposite manner, resulting in the dominant trophic group and trophic structure varying progressively from WM to GM to MDM. Soil properties but not vegetation determined the changes in trophic groups and trophic structure. The results implied that the higher trophic levels (carnivores or omnivores) responded more sensitively than the lower trophic levels (herbivores) to alpine wetland degradation. Our results also suggested that soil macrofauna have a habitat-specific characteristic trophic structure and can be used as indicators of soil health conditions.

•No notable effect from long-term warming on activity of nutrient-acquiring enzymes.

Microbes play an important role in the carbon cycle and nutrient flow of the soil ecosystem. However, the response of microbial activities to long-term warming over decades is poorly understood. To determine how warming changes ecoenzyme activity and microbial nutrient limitation, we conducted a long-term, 21 years, experiment, on the Qinghai–Tibet Plateau. We selected typical grass- and shrub-covered plots, used fiberglass open-top chambers (OTCs) to raise the temperature, conducted soil sampling at different depths, studied the response of nutrient-acquiring enzyme activity and stoichiometry, and conducted vector analysis of stoichiometry. Our results showed that long-term warming did not have a notable effect on the activity of nutrient-acquiring enzymes or enzymatic stoichiometry. However, Spearman correlation analysis indicated a significant and positive correlation between ecoenzyme activity and the available nutrients and microbial biomass in soil. Vector analysis of stoichiometry showed phosphorus limitation for all soil microbes at different depths, regardless of whether the soil experienced warming. These changes in enzymatic stoichiometry and vector analysis suggested that microbial nutrient limitation was not alleviated substantially by long-term warming, and warming did not considerably affect the stratification of microbial nutrient limitation. Our research has also shown that long-term warming does not significantly change soil ecoenzyme activity and original microbial nutrient limitation at different soil depths within the OTUsʼ impact range. These results could help improve understanding of microbial thermal acclimation and response to future long-term global warming.