Land-use effects on soil physicochemical properties, microbial biomass and respiration across soil depths in humid tropical ecosystems of Northeast India

Land-use change is a key driver of soil functional dynamics in tropical ecosystems, yet depth-resolved evidence across contrasting land-use systems remains limited in Northeast India. This study quantified variations in soil physicochemical properties, organic carbon, microbial biomass carbon (MBC), and soil respiration across four dominant land-use systems: managed monoculture Sal Plantations (SP), relatively undisturbed natural Mixed Forests (MF), semi-managed pineapple-based agroforestry systems (PBAS) and seasonal rain-fed agricultural systems (RFA) along 4 different soil profiles in Tripura. Soil samples from multiple depths were analyzed using linear mixed-effects models to account for land use, depth, and site-level variability. Land use significantly influenced most measured soil properties ( p < 0.05). Rain-fed agricultural systems exhibited 25–40% higher soil respiration and microbial biomass than forest systems. Soil depth also contributed to significant vertical variation in soil properties, whereas the interaction between land use and soil depth was generally weak. RFA soils were associated with higher soil temperature, moisture, bulk density, soil organic carbon, nutrient availability, microbial biomass carbon and soil respiration. In contrast, forest systems maintained a comparatively lower bulk density and more stable physical conditions, alongside moderate biological activity. The PBAS exhibited intermediate responses across physical, chemical, and biological attributes. Overall, these findings demonstrate that land-use systems strongly regulate soil physical, chemical, and biological functioning across soil profiles in humid tropical ecosystems. The land-use systems are closely linked to coordinated variations in soil structure, nutrient status, and microbial processes in humid tropical soils. The results underscore the relevance of agroforestry systems in moderating soil conditions relative to more intensive land use, while highlighting the importance of integrating soil depth into assessments of land-use impacts on soil functioning.