Elevation is one of the most influential factors affecting soil characteristics and microbial communities in forest ecosystems. Nevertheless, there is no consensus on how soil characteristics, soil microbials, and their relationships response to the elevation of the mountain ecosystem. We investigated the soil physicochemical characteristics, the activity of soil enzymes, and the microbial community at elevational sites from 600 to 2400 m above sea level (asl) in the western slopes of the Fanjing Mountain ecosystem, China. The soil microbial communities were determined by high throughput 16S rRNA and ITS amplicon sequencing. The results demonstrated that soil total nitrogen (TN) showed a slight decrease, whereas total phosphorus (TP) and total potassium (TK) gradually tended to increase with increasing elevation. The large macroaggregates (>2 mm) accounted for the largest proportion of the aggregate fraction (66.23%–76.13%) in the 0–10 cm soil layer with elevation. The average values of the soil electrical conductivity (EC), soil organic carbon (SOC), and cation exchange capacity (CEC) concentration in the 0–60 cm layer undulated with increasing elevation, and the highest values were observed at 1500–1800 m asl and 1800–2100 m asl, respectively. The activities of soil urease, sucrase, acid phosphatase, and catalase clearly differed (p < 0.05) with increasing elevation, and the minimum values were found at 2100–2400 m asl. Interesting, with increasing soil depth, the values of these factors tended to decrease, indicating surface aggregation. In addition, the soil microbial (bacterial and fungal) community diversity exhibited a single-peak pattern with elevation. Our results also revealed that the soil bacterial and fungal communities varied significantly at different elevation sites. The bacterial communities were dominated by the phyla Acidobacteria, Pseudomonadota, and Chloroflexi, and the phyla Basidiomycota and Ascomycota dominated the fungal communities. The Pearson and redundancy analyses revealed that the SOC, TP, four soil enzymes, and soil aggregates were significant factors influencing the soil microbial community. In conclusion, soil properties and enzyme activities jointly explained the elevational pattern of the soil microbial community in the Fanjing Mountain. The results of this study provide insights into the influence of elevation on soil characteristics, microbial communities, and their relationships in the Fanjing Mountain ecosystem.

Changes in altitude can cause regional microclimate changes, leading to the spatial heterogeneity of environmental factors and soil bacteria. However, the internal driving process and mechanism remain unclear. Here, we selected Fanjingshan, a typical nature reserve in the subtropical region of south China with a clear altitudinal belt, to reveal the response mechanisms of microbial populations with altitude changes. We examined the physiochemical and biological properties (pH and soil enzyme activities) of 0~10 cm soil layers, soil bacterial diversity, and community structure across the 2.1 km belt (consisting of six altitude ranges). Our results showed that soil pH was highest at the altitude range below 900 m and decreased with altitude thereafter. Soil enzyme activities showed an overall decreasing trend with altitude rising. The soil sucrase and catalase activity was highest (48.35 mg.g⁻¹.d⁻¹ and 23.75 µmol.g⁻¹, respectively) at altitudes below 900 m; the soil urease activity was highest (704.24 µg.g⁻¹.d⁻¹) at 900~1200 m; and the soil acid phosphatase activity was highest (57.18 µmol.g⁻¹) at 1200~1500 m. In addition, the soil bacterial community diversity showed a linear increasing trend, with the maximum abundance at 1500~1800 m. Soil pH was correlated with enzyme activity and bacterial community composition and structure, and the correlation was the strongest between pH and the distribution of bacterial diversity at altitudes below 900 m. Overall, soil enzyme activities and soil bacterial diversity showed spatial heterogeneity along the altitude gradient, and their community structure and composition were affected by altitude as a result of changes in soil physicochemical factors. This study provides a better and deeper understanding of the spatial succession of soil in the Fanjingshan area and the distribution pattern of soil microorganisms in central subtropical mountain ecosystems.

To respond to China’s policies of “balancing and supplementing high-quality farmland, converting dryland to paddy fields” and of improving the quality of drylands, large-scale dryland conversion to paddy fields has been recently implemented to improve farmland quality and increase grain production capacity in China. However, the effects of the conversions on the soil carbon (C) pool remain unclear. Therefore, in a karst area of Guizhou Province, China, we selected farmland soils that had undergone dryland-to-paddy conversion and planted with rice for one year, ensuring that the historical management practices, soil parent material, and spatial proximity were consistent. We compared changes in and interactions between soil physicochemical properties, organic C components, and the C pool management index (CPMI) in pre-conversion drylands, post-conversion paddy fields, and reference unused lands. We found that dryland-to-paddy conversion suppressed most soil physicochemical properties in the short term. After dryland conversion to paddy fields, total C, total organic C, dissolved organic C, easily oxidizable organic C, inert organic C, microbial biomass C, and soil CPMI significantly decreased temporarily. With conversion, the proportion of easily oxidizable organic C decreased, whereas those of dissolved organic C, microbial biomass C, and inert organic C increased. Correlation and redundancy analyses indicated that bulk density was negatively correlated with organic C, its components, and the CPMI, whereas soil nitrogen (N), alkaline N, available phosphorus (P), and available potassium were significantly positively correlated with organic C. The carbon pool activity and CPMI were primarily influenced by easily oxidizable organic C, microbial biomass C, alkaline N, and available P. According to a partial least squares structural equation model, soil physicochemical properties and organic C and its components were the main drivers of C pool changes. Organic C and its components directly influenced C pool changes, whereas soil physicochemical properties mostly indirectly influenced C pool changes. Therefore, although dryland-to-paddy conversion can maintain a balance of arable land and ensure food security, such conversions may lead to short-term declines in organic C stability and C pool management index, indicating mitigation strategies, such as tailored N, P, and K fertilization regimes, should be developed to increase farmland C sequestration capacity.