Climatic and topographic controls on soil organic matter storage and dynamics in the Indian Himalaya: Potential carbon cycle–climate change feedbacks

Abstract

Soil organic carbon (SOC) affects soil fertility and agricultural production, and SOC storage can also mitigate increasing atmospheric CO2 concentrations on decadal timescales or longer. SOC storage is dependent on climatic conditions, and changes in temperature and precipitation associated with climate change can influence soil processes leading to feedback mechanisms that help control atmospheric CO2 concentrations. Soils in tropical and subtropical mountain systems may be particularly sensitive to climate change, but SOC storage in high tropical and subtropical mountain regions is poorly quantified. To begin to evaluate the importance of C storage in soils in high mountain regions, regional SOC abundance was examined across the Himalaya of northern India. Soil samples were collected from the Kulu Lesser Himalaya, Lahul Himalaya, and Zanskar along an altitudinal and precipitation gradient of ~1900 to ~5000m above sea level and ~100 to ~900mmyr−1, respectively, and analyzed for SOC inventory as well as Δ14C and δ13C. The average annual SOC accumulation rates (between 1.9gm−2yr−1 and 47.3gm−2yr−1) and corresponding SOC turnover times (between ~50 and 3300years) were highly variable. The results show that SOC stocks in the Indian Himalaya are more sensitive to moisture availability than temperature, as average annual precipitation was a greater influence on SOC than altitude. Stable carbon isotope data indicate that C3 vegetation has been consistently dominant in the region for the last ~7000years. Rates of SOC accumulation and turnover are influenced greatly by variations in climate, vegetation, and topography. We conclude that increased precipitation may lead to increased SOC storage in the region, unless soils are exposed to greater erosion rates during intense storms.