The conversion of forests to agricultural land, primarily driven by human activities, is a key factor in land degradation. Although the impacts of land degradation on ecosystem functions are well-documented, the relationship between land degradation and carbon and nitrogen content, as well as certain biochemical indices, has not been thoroughly investigated. To fill this knowledge gap, this study examined the responses of microbial biomass, microbial respiration, and activity to soil organic carbon, soil depth, and land use change (LUC), from forest to agriculture. The research was conducted in three different land use types (Forest, Converted, and Agriculture) with two soil depths (0–30 and 30–60 cm) under uniform climatic and topographical conditions in the Northeastern Mediterranean Karst ecosystems along the southern coast of Türkiye. Analysis of a total of 180 soil samples showed that there are significant differences in the chemical and biochemical properties of soils according to land use type and soil depth. In particular, soil organic carbon, total nitrogen, microbial carbon, microbial nitrogen, and microbial respiration were higher in the topsoil (0–30 cm depth) of the forest areas. Agricultural areas, in contrast, exhibit significantly lower levels of SOC (10%), TN (10%), C mic (26%), N mic (17%), and MR (6%) compared to converted areas, placing them in the same group based on Tukey’s HSD test. Chemical and biochemical soil properties and stoichiometric indices in the study areas varied significantly with soil depth (Table [2](#tbl-cap-0002)) and showed a decreasing trend through soil depth except for CaCO 3 (%), C mic/N mic, and qCO 2. Our findings also reveal that stoichiometric indices, such as C mic/N mic and qMic, are highly sensitive indicators of land-use change. These findings indicate that human-induced land degradation negatively impacts carbon and nitrogen storage as well as sensitive microbial indicators in the topsoil.

Terrestrial ecosystems exhibit varied land uses as a result of both anthropogenic activities and natural processes. These variations in land use alter plant composition, soil characteristics, topography, management practices, and hence lead to significant differences in soil microbial communities and their properties. This study evaluated the impact of distinct land use types (riparian, forest, pasture) on soil microbial biomass and stoichiometric indices under uniform climatic and pedological conditions within a micro-basin in the Eastern Mediterranean region. The microbial biomass C (C mic) in the riparian area was observed to be 2.5 and 4 times lower than in the meadow and forest areas, respectively. Additionally, the microbial quotient ( qMic) in the riparian zone was 0.5 times higher compared to the forest and meadow areas. Stoichiometric indices, particularly qMic and metabolic quotient ( qCO 2), across all land uses, indicated that soils within this micro-basin were healthy and exhibited no signs of stress. The study further corroborated that land use exerts significant effects on soil microbial communities, with microbial biomass and activities largely influenced by soil organic matter. Notably, the C mic/N mic ratio remained within the range of 10-12 across all land uses, illustrating a fungal dominance in the microbial biomass. These findings underscore the role of land use patterns in altering soil properties, thereby influencing microbial biomass, microbial respiration, and stoichiometry in soils under similar environmental conditions.