Effects of aspect and changes in land use on organic carbon and soil properties in Uludere catchment, semi-arid region: Turkey

Response of soil organic carbon stocks and soil microbial biomass carbon to natural grassland conversion: A global meta-analysis

Natural grasslands worldwide are increasingly being converted into other land-use types, such as cropland and forest, thereby impacting soil carbon cycles and stocks. Soil organic carbon (SOC) is essential for regulating soil properties and microbial communities, while microbial biomass carbon (MBC) is the most active fraction of the SOC pool, both of which play pivotal roles in the global carbon cycle. Here, we performed a meta-analysis on 623 and 85 individual observations from 85 peer-reviewed articles to quantitatively evaluate the effect of grassland conversion on SOCS and MBC. Overall, conversions significantly reduced SOCS and MBC by 10.11 % and 30.63 %, respectively. Notably, the impact varied by conversion type: converting grassland to forest, cropland, and plantation reduced SOCS by 7.69 %, 16.47 %, and 20.55 %, respectively. Meanwhile, converting grassland to cropland and abandoned land decreased MBC by 47.80 % and 38.74 %, respectively. Environmental factors such as mean annual temperature (MAT), mean annual precipitation (MAP), soil total nitrogen (TN), and soil carbon-to‑nitrogen ratio (C/N) influenced these changes. SOCS and MBC were positively correlated with MAT, soil C/N and TN. Specifically, when the C/N or TN of the converted soil exceeded 1.21 or 1.11 times that of the original grassland, SOCS would exhibit a trend of carbon sequestration. Our findings provide valuable insights for global soil carbon sequestration and land use management policies.

Changes of SOC Content in China’s Shendong Coal Mining Area during 1990–2020 Investigated Using Remote Sensing Techniques

Coal mining, an important human activity, disturbs soil organic carbon (SOC) accumulation and decomposition, eventually affecting terrestrial carbon cycling and the sustainability of human society. However, changes of SOC content and their relation with influential factors in coal mining areas remained unclear. In the study, predictive models of SOC content were developed based on field sampling and Landsat images for different land-use types (grassland, forest, farmland, and bare land) of the largest coal mining area in China (i.e., Shendong). The established models were employed to estimate SOC content across the Shendong mining area during 1990–2020, followed by an investigation into the impacts of climate change and human disturbance on SOC content by a Geo-detector. Results showed that the models produced satisfactory results (R2 > 0.69, p < 0.05), demonstrating that SOC content over a large coal mining area can be effectively assessed using remote sensing techniques. Results revealed that average SOC content in the study area rose from 5.67 gC·kg−1 in 1990 to 9.23 gC·kg−1 in 2010 and then declined to 5.31 gC·Kg−1 in 2020. This could be attributed to the interaction between the disturbance of soil caused by coal mining and the improvement of eco-environment by land reclamation. Spatially, the SOC content of farmland was the highest, followed by grassland, and that of bare land was the lowest. SOC accumulation was inhibited by coal mining activities, with the effect of high-intensity mining being lower than that of moderate- and low-intensity mining activities. Land use was found to be the strongest individual influencing factor for SOC content changes, while the interaction between vegetation coverage and precipitation exerted the most significant influence on the variability of SOC content. Furthermore, the influence of mining intensity combined with precipitation was 10 times higher than that of mining intensity alone.