Carbon and Nitrogen Contents in Typical Plants and Soil Profiles in Yanqi Basin of Northwest China

Carbon and nitrogen are the most important elements in the terrestrial ecosystem. Studying carbon and nitrogen distributions in plant and soil is important for our understanding of the ecosystem dynamics and carbon cycle on arid lands. A study was conducted in a typical arid area, the Yanqi Basin, Northwest China. Carbon and nitrogen distributions in plant tissues and soil profiles were determined at 21 sites with typical native plants and crops. Our results indicated that carbon content was similar between crops and native plants, and the average carbon contents in aboveground (42.4%) and belowground (42.8%) tissues were almost the same. Average nitrogen contents in crops were nearly the same (similar to 0.7%) in aboveground and belowground tissues whereas mean nitrogen content was approximately 100% higher in aboveground (2.2%) than in belowground (1.2%) tissues for native species. Soil organic carbon (SOC) and total nitrogen (TN) in cropland (9.4 and 0.9 g kg(-1)) were significantly higher than those in native land (6.2 and 0.7 g kg(-1)). Multiple regression analyses indicated that carbon content in belowground tissue and nitrogen content in aboveground tissue were key factors connecting plant and soil in native land. However, there was no significant relationship for carbon or nitrogen between soil and crop, which might reflect human disturbance, such as plowing and applications of various organic materials.