Soil organic carbon stabilization changes with an altitude gradient of land cover types in central Himalaya, India

Abstract

Soil organic carbon (SOC) stabilization in a mountain forest ecosystem is a key component of the global carbon cycle to mitigate the rising level of atmospheric carbon dioxide. We investigated the effects of different types of land cover at different altitudes on SOC stabilization in the Himalayan region, India. We chose four different land covers at different altitudes, viz., pasture land (~2500 m), mixed cover (~2200 m), chirpine (~950 m) and agricultural land (~950 m). Organic carbon (OC), total nitrogen (N), and total microbial activity (MAt) in soils up to depths of 100 cm and under different types of land cover were assessed to study the impact of vegetation cover on the storage of SOC and N. Hydrofluoric acid (HF) soluble carbon, FeDCB/AlDCB oxides and stable carbon isotopes (δ13C) were determined in the soils under different types of land cover to evaluate the amounts of mineral-associated carbon and understand the organic carbon stabilization process. The maximum SOC stock was observed under a mixed land cover (281.86 t ha−1), followed by pasture land cover (229.61 t ha−1), chirpine (182.16 t ha−1) and agricultural land cover (70.20 t ha−1) up to a depth of 100 cm. Higher SOC contents, N contents and MAt were closely linked to the surface layers (0–30 cm), while HF-soluble carbon, FeDCB and AlDCB oxides were linked to sub-surface layers (30–100 cm) of soils under different types of land cover. HF-soluble carbon was more abundant in mixed and pasture land covers compared with chirpine and agricultural land covers. The linear relationship between δ13C values and HF-soluble carbon, FeDCB/OC, δ13C, AlDCB/OC and δ13C in soils under mixed and pasture land covers confirmed that the subsurface soil constituted more decomposed carbon and its associated FeDCB/AlDCB minerals. Nevertheless, this trend was not observed in other types of land cover located at lower altitudes and might be due to the root exudates and/or mixing of young and old carbon. These results suggest that the land cover types at higher altitudes in central Himalaya may be considered as a potential sink for the sequestration of atmospheric carbon and as potential sites for the stabilization of sequestered carbon in soils. However, land cover types at lower altitudes in central Himalaya must be managed by better soil management practices to sequester and stabilize more carbon in soils.