Spatial variations and influencing factors of soil organic carbon under different land use types in the alpine region of Qinghai-Tibet Plateau

Abstract

Understanding soil organic carbon (SOC) distribution and influencing factors are important to accurately assess soil carbon sink potential and ecosystem quality. However, variations and controls of SOC content and stock under various land use types in the alpine region of Qinghai-Tibetan Plateau remain challenging. In this study, soil properties (pH, bulk density, porosity, clay content, soil organic carbon, soil water content, total nitrogen, total phosphorus, available nitrogen and available phosphorus) and environmental parameters (annual average temperature, annual average rainfall, normalized differential vegetationindex, altitude, slope, surface roughness, longitude and latitude) were determined across a 600 km east–west transect in the Tibet alpine region for investigating the distribution characteristics and controls of SOC for three land use patterns — farmland (FA), forestland (FO) and grassland (GR). Results indicated that SOC content in the 0–30 cm decreased with increasing soil depth at different reduction rates under various land use types. The average SOC content and stock in GR was significantly higher than that in FO and FA due to the existence of mattic epipdon in GR under high altitude. The non-consideration of gravel content in soil can lead to an overestimation of SOC stock of 0–30 cm soil layer by 15.37 %, 16.70 % and 17.43 % for FA, FO and GR, respectively. Soil properties and environmental conditions simultaneously affect the spatial distribution of SOC under various land use patterns. Pedotransfer functions (PTFs) using multiple regression were used to forecast SOC content in the studied alpine region, which had a better predictive performance than previous published PTFs in the plain area, especially when SOC contents were higher than 40 g kg−1. Our study provides a foundation to build SOC prediction models for other alpine regions in the world, where SOC contents generally exhibit a wider range than the plain areas.