放牧强度对黄土丘陵区生物结皮土壤化学计量学特征的影响

研究以位于黄土丘陵区的固原、定边、神木、安塞为研究区域，以各区20年以上封禁草地（G0）为对照，分析了不同放牧强度（以羊粪球密度计：G1，0~10个·m^-2；G2，10~20个·m^-2；G3，>20个·m^-2）下生物结皮层及0~2 cm土层土壤有机碳（SOC）、全氮（TN）、全磷（TP）含量及生态化学计量学特征。结果表明：放牧仅降低安塞藓结皮盖度，对各地区的藻结皮盖度和生物量均无影响；从各区域来看，除神木生物结皮层和0~2 cm土层SOC、TN、N：P、C：P在G3下降低以外，其余地区各放牧强度下SOC、TN、TP含量及C：N、N：P、C：P无降低现象；总体来看，各强度放牧对生物结皮层SOC、TN、TP含量及C：N、N：P、C：P无影响，对0~2 cm土层SOC、TN、TP含量及C：N无影响，而N：P、C：P在G3降低。综上，放牧强度小于G3时，黄土丘陵区退耕草地生物结皮土壤养分及生态化学计量学特征无降低现象。

Effects of Grazing Intensity on Stoichiomerty of Biological Soil Crusts in the Hilly Loess Plateau region

Guyuan,Dingbian,Shenmu and Ansai were selected as the study areas in the hilly Loess Plateau region. The closed rehabilitated grasslands (G0) that over 20 years old was set as the control,the effects of grazing in different intensity on soil organic carbon (SOC),total nitrogen (TN),total phosphorus (TP) contents and ecological stoichiometry characteristics of biocrusts at 0~2 cm layer soil were investigated in the rehabilitated grasslands of the hilly Loess Plateau region. Three grazing intensity,G1:0~10 goat dung·m^-2,G2:10~20 goat dung·m^-2 and G3:>20 goat dung·m^-2,were included in the study. The results showed that the coverage of moss crusts decreased against the increase of grazing intensity in Ansai. In addition,grazing intensity did not exert significant effects on the coverage and biomass of cyanobacterial and moss crusts in the three other study areas. SOC,TN,N:P and C:P decreased under the intensity of G3 in Shenmu. Moreover,SOC,TN,TP,C:N,N:P and C:P did not show an obvious decrease under different grazing intensities in the three other areas. In general,grazing did not significantly affect the contents of SOC,TN,TP,C:N,N:P and C:P at the biocrustal layer in the hilly Loess Plateau region,and did not significantly affect the contents of SOC,TN,TP and C:N at 0~2 cm soil layer,but in comparison with no grazing,N:P and C:P were decreased at G3. In conclusion,when the grazing intensity was lower than G3,the soil nutrient and ecological stoichiometry characteristics of biological soil crusts were not reduced in the rehabilitated grassland of the hilly loess region.