Divergent contribution of environmental factors to soil organic and inorganic carbon in different land use types in a forest-grassland ecotone of Inner Mongolia, China

Abstract

Understanding the comprehensive impacts of environmental factors on soil organic carbon (SOC) and soil inorganic carbon (SIC) in different land use types is of great significance for sustainable soil management. Least absolute shrinkage and selection operator (LASSO) and structural equation modelling were applied to reveal the driving mechanism of SOC, SIC and the ratio between SOC to SIC (SOC/SIC) in three major land use types (forest, grassland and farmland) in a forest-grassland ecotone (FGE) of Inner Mongolia, Northeast China. Mean annual temperature (MAT), mean annual temperature (MAP) and Enhanced Vegetation Index (EVI) were selected by LASSO as the three most important environmental factors affecting SOC, SIC and SOC/SIC in all land use types. MAT had the strongest direct effects on SOC in forest and grassland among all the environmental factors, suggesting temperature was the most important control factor of SOC in forest and grassland. EVI had relatively strong indirect effects on SOC by influencing total nitrogen and total phosphorus in grassland and farmland, respectively. MAT and MAP had significantly direct effects on SIC in all land use types, demonstrating the balance between precipitation and evapotranspiration affected by temperature were the major control factors of SIC. In addition, MAT had significantly positive direct effects (>42%) on SOC/SIC in all land use types, suggesting climate warming can have positive feedbacks on the proportion of SOC in the soil carbon pool in FGE. This study provides a comprehensive understanding of the driving mechanism of SOC, SIC and SOC/SIC in FGE of Northeast China.

Keywords: Forest-grassland ecotone; Land use types; Soil inorganic carbon; Soil organic carbon; Structural equation modelling.