Soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest in southwestern India

Severin-Luca Bellè,Jean Riotte,Muddu Sekhar,Laurent Ruiz,Marcus Schiedung,Samuel Abiven

doi:10.1016/j.geoderma.2021.115606

Abstract

Soil organic carbon is regulated by a dynamic interaction of vegetation inputs, organic matter degradation and stabilization processes in soils, and its redistribution in the landscape. Tropical ecosystems are highly important in terms of carbon stored in vegetation and soil, but many processes of the soil carbon cycle in the tropics are yet to be fully understood. Here, we studied soil organic carbon stocks and quality in small-scale tropical, sub-humid and semi-arid watersheds along a climate gradient in southwestern India with varying vegetation and geology to identify major drivers of soil organic carbon dynamics in three prevalent soil types (Lixisol, Vertisol and Ferralsol) under shrubland and dry deciduous forest. We used a combination of organic carbon analysis (total organic carbon content, 13C, C:N), mid-infrared spectroscopy and soil property information (bulk density, texture, oxides, pH, cation-exchange capacity). Soil organic carbon stocks in these watersheds showed a substantial range from 58.2 to 169.4 MgCha−1 in the first 60 cm, and the differences depended on local- to watershed-scale variations in vegetation type and history, geology, soil physio-chemical (clay, oxides) and biological (bioturbation) properties. Considerable parts of the organic carbon stored in these soils was found below 30 cm (up to 40%), stressing the importance of tropical subsoils. From our analysis of the soil organic carbon quality and literature data on paleoclimate and vegetation, we could identify land-use changes in these watersheds, from tropical moist evergreen forests, forest-savannah transitions and plantations to secondary regrowth forest over time. Our study provides new data and insights into the local-scale drivers of soil organic carbon quantity and quality of tropical, sub-humid and semi-arid watersheds under shrubland and dry deciduous forest with varying geology and soil types.

Highlights

Soils are a key component of the global carbon (C) cycle and are the major storage of biomass-derived organic carbon on Earth
soil organic carbon (SOC) stock differences between soils under open-mixed shrubland/forest and dry deciduous forest can be explained by the present-day vegetation density, composition and productivity that is higher in forests, which determines the quantity and composition of plant litter inputs (Beer et al, 2010; Carvalhais et al, 2014; Proulx et al, 2015), and the vegetation history of the studied watersheds
The SOC stocks in three small-scale sub-humid and semi-arid watersheds in southwestern India showed a large range from 58.2 to 169.4 Mg ha−1 in the first 60 cm, with differences depending on vegetation type and history, geology and soil properties

Summary

Introduction

Soils are a key component of the global carbon (C) cycle and are the major storage of biomass-derived organic carbon on Earth. Tropical ecosystems store 288 and 480 Pg C in soils under grassland/savannah and forest respectively (0–300 cm), and make up approximately one third of. Estimates of SOC stocks for tropical and subtropical forests can range from 94 to 143 Mg ha−1 (0–100 cm; (Duarte-Guardia et al, 2019)) to 239 Mg ha−1 (0–300 cm; (Carvalhais et al, 2014)). Tropical grassland/savannah store between 99 and 104 Mg ha−1 (0–100 cm; (Duarte-Guardia et al, 2019)) and 151 Mg ha−1 (0–300 cm; (Carvalhais et al, 2014))

Methods

Results

Conclusion