Understanding carbon sequestration and its correlation with macronutrients and physical parameters in semi-arid ecosystems - A comparative study of Prosopis, forest and grassland soils

Abstract

Soil plays a critical role in the cycling of carbon and nutrients, acting as the largest carbon pool in terrestrial ecosystems by storing, recycling, and releasing carbon. Semi-arid regions (SARs) characterised by limited rainfall and high evapotranspiration rates have traditionally been overlooked in carbon assessments due to their relatively minor role in the global carbon sink. However, their rapid expansion and dominance in carbon sink trends and interannual variability make them vital to global carbon dynamics. This study examines the vertical distribution of soil properties and their correlation with carbon sequestration across three predominant vegetation types- Prosopis invaded, grassland and forest in the SARs of Andhra Pradesh and Karnataka.

Soil samples were collected at four depth intervals (0-15 cm, 15.1-30 cm,30.1- 60 cm and 60.1-90 cm) and analysed for pH, electrical conductivity (EC), bulk density (BD), soil organic carbon (SOC), nitrogen, phosphorus and potassium. Significant differences were observed in all parameters with vegetation type, while pH, SOC, nitrogen, and potassium also showed significant differences with depth. SOC, nitrogen and potassium decreased with depth, likely due to reduced organic matter and microbial activity, while salinisation and leaching lowered pH at surface layers. Nitrogen and depth were key factors in carbon sequestration, with nitrogen increasing storage through its link to organic matter, while depth reduced SOC due to less organic matter at greater depths. SOC and nitrogen levels were highest in forest soils, then in grasslands, and lowest in Prosopis ecosystems. In contrast, pH, EC, BD, phosphorus and potassium were highest in Prosopis ecosystems, indicating the species’ adaptability and invasive success. These findings emphasise the need for deeper sampling and ecosystem-level studies to better understand carbon dynamics, particularly in the context of land use changes and invasive species proliferation.