Fazhu Zhao;Lu Zhang;Jian Sun;Chao Ren;Xinhui Han;Gaihe Yang;Guowei Pang;Haiyan Bai;Jun Wan

College of Urban and Environmental Sciences, Northwest University, Xi'an 710127 (China);Shaanxi Land Construction Group, Shaanxi LCG Land Project Technology Institute, Key Laboratory of Degraded and Unused Land Consolidation Engineering, the Ministry of Land and Resources of China, Xi'an 710075 (China);Institute of Agricultural Resources and Environment, Ningxia Academy of Agriculture and Forestry Sciences, Yinchuan 750002 (China);College of Agronomy, Northwest A&F University, Yangling 712100 (China);College of Urban and Environmental Sciences, Northwest University, Xi'an 710127 (China

soc fractions;soil depths;soil c;cm;n:p ratios;0

Afforestation is recognized as an important driving force for soil organic C (SOC) dynamics and soil element cycling. To evaluate the relationships between soil C:N:P stoichiometry and SOC fractions, soil C:N:P stoichiometry distributions at 0-200 cm soil depths were analyzed and the contents of SOC fractions were evaluated in 9 typical land-use systems on the Loess Plateau of China. The contents of light fraction organic C, particulate organic C (> 53, 53-2 000, and > 2 000 mu m), labile organic C, microbial biomass C, and dissolved organic C decreased with increasing soil depth and were higher in afforested soil than in slope cropland soil. Compared with the slope cropland, different vegetation types influenced soil C:N, C:P, and N:P ratios, especially when C:P and N:P ratios were significantly higher (P < 0.05). Moreover, SOC fractions at the 0-10 and 10-40 cm depths were particularly affected by soil C:P ratio, whereas those at the 40-100 and 100-200 cm soil depths were significantly affected (P < 0.05) by soil N:P ratio. These results indicate that changes in SOC fractions are largely driven by soil C:P and N:P ratios at different soil depths after afforestation.