Patterns and Controls of Soil Organic Carbon and Nitrogen in Alpine Forests of Northwestern China

Soil carbon (C) and nitrogen (N) in high-altitude forests are of special interest because of high concentrations and potential feedback to climate warming. However, the patterns and environmental controls on C and N storage are poorly known. Here, we determined the distribution of soil organic carbon (SOC) and total nitrogen (TN) along the elevation gradient in the Picea crassifolia forests of the Qilian Mountains in northwestern China and explored their environmental control factors. Our results showed that SOC stocks increased significantly with elevation and ranged from 18.83 to 31.09 kg m(-2) at a soil depth of 0 to 50 cm; these C estimates were greater than those for other temperate forests. Total N stocks ranged from 1.07 to 3.14 kg m(-2) at a soil depth of 0 to 50 cm and did not exhibit significant increases with elevation. In the P. crassifolia forests, understory vegetation and soil texture, especially clay content, along with climatic factors, played an important role in controlling the distribution of SOC stocks. We found that SOC stocks decreased with temperature and increased with precipitation. These results led us to the conclusion that climate warming together with a decline in precipitation would reduce soil C storage in these forests.