Differences in land use type and chronological age affect soil properties and plant community characteristics, which may influence soil structural stability and erodibility. However, knowledge on the effects of soil physicochemical properties on soil aggregate stability and erodibility at different land use years is limited. This study selected five land use types: corn field (Year 38^th-y), corn intercropped with cabbage field (Year 38^th-y + b), fruit and meridian forest (Year 6^th-jgl), naturally restored vegetation (Year 6^th-zr), and artificial forest (Year 7^th-rgl) in the karst landscape of the Chishui River Basin in Yunnan Province. We aimed to identify the influencing factors of soil stability and erodibility under different land use time series. The results indicated that the mean weight diameter (MWD), the geometric mean diameter (GMD), and soil structural stability index (SSI values) were highest in Y6^th-zr and lowest in Y7^th-rgl. Conversely, the erodibility K value was lowest in Y6^th-zr, suggesting that the soil structure in Y6^th-zr exhibited greater stability, whereas soil stability in Y7^th-rgl was lower. Redundancy and throughput analyses revealed that organic carbon and water-stable aggregates > 2.0 mm content had higher vector values. Soil bulk density, total nitrogen, organic carbon, and soil texture content were the main factors contributing to soil stability variation (0.338–0.646). Additionally, total nitrogen, organic carbon, total phosphorus, and soil texture content drove the variation in K values (0.15–1.311). Natural vegetation restoration measures can enhance soil structure to a certain extent. These findings highlight changes in soil aggregate stability and erodibility over different land use durations. The research results have important theoretical and practical significance for understanding the differences in soil erosion and soil restoration under different land use patterns in the karst landscapes of southwest China.

Increased nitrogen deposition profoundly impacts ecosystem nutrient cycling and poses a significant ecological challenge. Soil microorganisms are vital for carbon and nutrient cycling in ecosystems; however, the response of soil microbial communities in subtropical planted coniferous forests to nitrogen deposition remains poorly understood. This study carried out a four-year nitrogen addition experiment in the subtropical montane forests of central Yunnan to explore the microbial community dynamics and the primary regulatory factors in two coniferous forests (P. yunnanensis Franch. and P. armandii Franch.) under prolonged nitrogen addition. We observed that nitrogen addition elicited different responses in soil bacterial and fungal communities between the two forest types. In P. yunnanensis Franch. plantations, nitrogen supplementation notably reduced soil bacterial α-diversity but increased fungal diversity. In contrast, P. armandii Franch. forests showed the opposite trends, indicating stand-specific differences. Nitrogen addition also led to significant changes in soil nutrient dynamics, increasing soil pH in P. yunnanensis Franch. forests and decreasing it in P. armandii Franch. forests. These changes in soil nutrients significantly affected the diversity, community structure, and network interactions of soil microbial communities, with distinct responses noted between stands. Specifically, nitrogen addition significantly influenced the β-diversity of fungal communities more than that of bacterial communities. It also reduced the complexity of bacterial interspecies interactions in P. yunnanensis Franch. forests while enhancing it in P. armandii Franch. forests. Conversely, low levels of nitrogen addition improved the stability of fungal networks in both forest types. Using random forest and structural equation modeling, soil pH, NH4⁺-N, and total nitrogen (TN) were identified as key factors regulating bacterial and fungal communities after nitrogen addition. The varied soil nutrient conditions led to different responses in microbial diversity to nitrogen deposition, with nitrogen treatments primarily shaping microbial communities through changes in soil pH and nitrogen availability. This study provides essential insights into the scientific and sustainable management of subtropical plantation forest ecosystems.

As the fundamental unit of soil structure, soil aggregates play a crucial role in enhancing soil carbon and nitrogen storage, thereby supporting soil fertility and overall health, particularly in fragile karst regions. This study aims to quantify the effects of various ecological construction measures on soil aggregate stability, including focusing on geometric mean diameter (GMD), mean weight diameter (MWD), and K values, as well as aggregate-related organic carbon (SOC) and total nitrogen (TN), soil mechanical composition, and aggregate content. The ecological construction measures examined include plantation forests (Y7th–rgl), restored forests (Y6th–zr), fruit forests (Y6th–jgl), and contour reverse slope terraces (Y1th–crt). Compared to sloping farmland, contour reverse slope terraces, with their distinctive priority induction function, significantly increased the content of medium-fine particle aggregates, greater than 87%. Among the ecological construction measures, plantation forests exhibited the highest aggregate stability, with an average increase ranging from 8% to 157%. Notably, microaggregates, regardless of size, possessed the highest carbon and nitrogen contents, contributing significantly to soil carbon and nitrogen pools. Furthermore, both plantation and contour reverse slope terrace treatments demonstrated an equal contribution of carbon and nitrogen across all aggregate sizes. The partial least squares path modeling (PLS-PM) analysis indicates that land use type and the content of carbon and nitrogen pools are the primary factors influencing soil aggregate stability. These findings suggest that plantations are particularly effective in enhancing soil and water conservation in fragile karst areas, while the contour reverse slope terrace method shows potential for stabilizing soil structure over extended time scales due to its unique “preferential entrainment” function.

The rapid increase in reactive nitrogen (N) released into the environment by human activities has notably altered the structure and composition of forest soil microbial communities (SMCs), profoundly impacting the N cycle in terrestrial ecosystems. However, the response of soil microorganisms to nitrogen addition in different seasons is not clear. This study delved into how SMCs in a subtropical region of central Yunnan, China, specifically in an evergreen broad-leaved forest (EBLF), respond to N deposition during both the dry and wet seasons. Through high-throughput sequencing, we assessed the composition and structure of SMCs under varying N addition treatments across seasons, examining their interplay with soil chemical properties, enzyme activities, and community responses. The findings revealed significant outcomes following four years of N addition in the subtropical EBLF: (1) Significant changes were observed due to the interaction between N addition and seasonal changes. Soil pH significantly decreased, indicating increased soil acidification, particularly in the dry season. Increased moisture in the wet season mitigated soil acidification. (2) In the dry season, N addition led to a decrease in microbial richness and diversity. In the wet season, N addition increased microbial richness and diversity, alleviating the downward trend observed in the dry season. (3) N addition significantly impacted the composition of soil bacterial and fungal communities. Dominant fungal genera in the wet season were particularly sensitive to N addition. (4) Seasonal changes and N addition altered soil microbial community structures. Soil chemical properties and enzyme activities significantly influenced the microbial community structure. However, due to differences in soil moisture, the key environmental factors that regulate microbial communities have changed significantly during the dry and wet seasons. This study serves as a foundation for understanding how N deposition impacts SMCs in EBLF ecosystems in subtropical regions, offering valuable insights for the scientific management of forest ecological resources amidst global change trends.

Atmospheric nitrogen deposition has a profound impact on soil nitrogen (N) cycling within terrestrial ecosystems, altering the microbial community structure and composition. To investigate how nitrogen deposition impacts microbial communities across different seasons, this study focused on a mature subtropical Quercus aquifolioides forest. Four nitrogen treatments were applied, and high-throughput sequencing was utilized to analyze soil microbial composition and structure changes during dry and wet seasons. Additionally, the study explored the interactions between soil nutrients, microbial communities, and nitrogen treatments. Following four years of nitrogen supplementation, the results revealed that: (1) Soil chemistry and enzyme activity shifted significantly due to the combined effects of nitrogen addition and seasonal variations. A marked reduction in soil pH indicated substantial acidification, although the wet season’s increased soil moisture mitigated these effects. (2) Fungal richness and diversity were more sensitive to nitrogen addition than bacterial diversity. (3) During the wet season, nitrogen deposition caused notable shifts in soil microbial community composition, with a notable elevation in the relative proportion of the fungal genus Sebacina (↑112.68%) under MN treatment. (4) Nitrogen addition affected the co-occurrence network complexity of soil bacteria and fungi in a season-dependent manner. During the dry season, bacterial network complexity decreased significantly while fungal network complexity increased. In contrast, the wet season showed an elevation in bacterial network complexity and a reduction in fungal network complexity. (5) The fungal community structure remained stable across seasons and nitrogen treatments, whereas the bacterial community structure showed significant differences after nitrogen addition. Environmental factors influencing bacterial and fungal community structures varied depending on water conditions. These findings provide insights into forest soil management and microbial remediation strategies in response to future atmospheric nitrogen deposition.

This study hypothesized that different base fertilizer application has different effects on improving the efficiency of maize water utilization and promoting maize growth. Utilizing field positioning sloping farmland micro-zone experiments, six distinct types of base fertilizers were designed: a control group without fertilization (CK), chemical fertilizer alone (T1), a mixture of local farmyard manure (40% pine needles and 60% livestock manure, T2), a 50% reduction in chemical fertilizer combined with farmyard manure (T3), the incorporation of crushed straw through deep plowing (T4), and the fermentation of crushed straw mixed with urea before field application (T5). The results indicate that, compared to the CK treatment, the T3 and T5 treatments significantly enhanced soil moisture content, with increases ranging from 4.06% to 18.67% during the normal year (2023) and the drought year (2024), respectively. Additionally, the water utilization efficiency of maize was improved significantly, with values of 35.38% and 41.54%, and the yield increased by 12.30% to 25.92%. The maize yields under T3 and T5 treatments reached 12.19 and 13.31t/ha, respectively. Therefore, we propose that crushing straw and incorporating urea and water for fermentation as a base fertilizer in maize fields can ensure efficient water use in this region, leading to higher yields.