Changes in vegetation influence the function of grassland ecosystems. A degradation of the vegetation type has been found from high to low altitudes in Guanshan grassland in the order of forest grassland (FG) < shrub grassland (SG) < herb grassland (HG). However, there is poor information regarding the effect of vegetation degradation on soil microbes in Guanshan grassland. Therefore, our study evaluated the impact of vegetation degradation on the microbial parameters of soil, as well as the mechanisms responsible for these variations. Soils were sampled from 0 to 30 cm under the FG, SG, and HG in Guanshan grassland for determining the microbial biomass, enzymatic activities, basal respiration (BR), and metabolic quotient (qCO₂) in April and July 2017. The results showed that vegetation types are important factors that obviously influence the above-mentioned soil microbial properties. The FG and SG had significantly higher soil microbial biomass, enzymatic activities, and BR than those of the HG, but markedly lower qCO₂ (p < 0.05). Soil pH, available nitrogen (AN), organic carbon (SOC), total phosphorus (TP), available P (AP), and total N (TN) were key factors in the decline in the soil microbial biomass and microbial activities of the degraded vegetation. Moreover, slope aspects also affected the soil microbial properties, with the east slope having higher soil microbial biomass, enzymatic activities, and BR and lower qCO₂ than the west slope. Conclusively, vegetation degradation has led to a decline in the soil microbial biomass and microbial activities, indicating the degradation of the Guanshan grassland ecosystem.

Cadmium (Cd) is a toxic metal and found in various soils, including forest soils. The great spatial heterogeneity in soil Cd makes it difficult to determine its distribution. Both traditional soil surveys and spatial modeling have been used to study the natural distribution of Cd. However, traditional methods are highly labor-intensive and expensive, while modeling is often encumbered by the need to select the proper predictors. In this study, based on intensive soil sampling (385 soil pits plus 64 verification soil pits) in subtropical forests in Yunfu, Guangdong, China, we examined the impacting factors and the possibility of combining existing soil information with digital elevation model (DEM)-derived variables to predict the Cd concentration at different soil depths along the landscape. A well-developed artificial neural network model (ANN), multi-variate analysis, and principal component analysis were used and compared using the same dataset. The results show that soil Cd concentration varied with soil depth and was affected by the top 0–20 cm soil properties, such as soil sand or clay content, and some DEM-related variables (e.g., slope and vertical slope position, varying with depth). The vertical variability in Cd content was found to be correlated with metal contents (e.g., Cu, Zn, Pb, Ni) and Cd contents in the layer immediately above. The selection of candidate predictors differed among different prediction models. The ANN models showed acceptable accuracy (around 30% of predictions have a relative error of less than 10%) and could be used to assess the large-scale Cd impact on environmental quality in the context of intensifying industrialization and climate change, particularly for ecosystem management in this region or other regions with similar conditions.

Introduction: Mycobacterium bovis , the causative agent of zoonotic tuberculosis, poses a serious threat to public health and agriculture. This study investigates the antibacterial activity and mechanism of action of isocorydine (ICD), a natural alkaloid from Dicranostigma leptopodum (Maxim.) Fedde ( DLF ), against M. bovis . Methods: The minimum inhibitory concentration (MIC) of ICD was determined. Phenotypic changes were assessed through assays measuring cell wall/membrane integrity, ion leakage, extracellular pH, total lipid content, and electron microscopy. The global response of M. bovis to sub-inhibitory ICD was elucidated using transcriptomic and metabolomic profiling. Results: ICD exhibited potent antibacterial activity with a MIC of 400 μg/mL. It disrupted the cell wall and membrane, leading to ion leakage, pH alteration, reduced lipids, and severe ultrastructural damage. Transcriptomics revealed 66 differentially expressed genes, with significant upregulation of efflux pumps and TetR family regulators. Metabolomics identified 1,158 differential metabolites, indicating a profound metabolic rewiring characterized by depleted central carbon metabolites and accumulated fatty acids. Discussion/conclusion: Our results demonstrate that ICD exerts its antibacterial effect primarily by targeting the cell envelope, causing membrane disruption and energetic stress. M. bovis responds by activating efflux pumps and reprogramming its metabolism. This multi-omics study reveals the potential of ICD as an anti-mycobacterial agent and provides novel insights into the adaptive strategies of M. bovis under phytochemical stress.

Biocrusts occupy the surface of soils, house key microbes and non-vascular plants, and further provide other vital ecological functions in oligotrophic drylands. However, little is known about the impact of trampling on fragile biocrusts in temperate deserts, particularly changes to soil microbial communities. To examine this, fresh soils from three trampled intensities to biocrusts were sampled in vegetation areas of the Tennger Desert. Soil microbial biomass carbon and nitrogen, and microbial communities were studied using chloroform fumigation and Illumina sequencing, respectively. The results collected 2050 OTUs and 393 species of bacterial communities and 1124 OTUs and 135 species of fungal communities. Severe trampling of biocrusts resulted in a reduction in soil microbial biomass carbon and nitrogen, and soil microbial abundance and diversity; changed the relative abundance of microbial taxa; altered the soil microbial community structures of cyanobacteria-dominated crusts, and further affected microbial community functions. Reduced soil moisture and nutrients and enhanced pH were the factors which caused alteration in soil microbial communities after trampled biocrusts. In addition, there was a negative correlation between trampling intensity with soil nutrient content, soil microbial biomass carbon and nitrogen, and microbial abundance. After similar trampling intensity, later-succession moss-dominated crusts were significantly higher in soil nutrients, soil microbial biomass carbon and nitrogen, soil fungal abundance and diversity, and more distinctive microbial community structures compared to early-succession cyanobacteria-dominated crusts. This suggests that there is a positive correlation between biocrust tolerance to trampling and the successional stages of biocrusts. Therefore, severe trampling of biocrusts could modify biocrust fragile structures and functions, which in turn, altered soil microbial community compositions and structures, and discouraged their function, leading to a degradation process of surface soils in temperate desert ecosystems.