The Characteristics And Mechanisms Of Stable Carbon Isotope In Degraded Grasslands

The experiment was carried out in the seven types of Chinese grasslands in August 2014,and analyzed samples within the next year.We attemped to investigate the stable carbon isotopes(δ¹³C)variation characters of leaves,roots and soil in degraded grassland,and to reveal the mechanism of factors effecting on δ¹³C values:grazing（grazing treatment and grazing intensity）and geographical factors（longitude,latitude and altitude）.This experiment provides a new idea and method for monitoring grassland degradation.The results are as follows:（1）The δ¹³C range values of leaves,roots and soils in all types of grassland were unique.The variation degree of δ¹³C1eaf range value at different families and the range value of δ¹³Croot were both increased after grazing,and the later become more negative.While the variation of δ¹³Csool range values at different depths and after grazing were both not in one direction.（2）Overgrazing caused most δ¹³Cleaf values decreasing and the photosynthetic pathway of three species converting,but have little effect on δ¹³Croot values.The four factors,grazing treatments,depths,regions,the interaction between grazing treatments and regions,were significantly effected the δ¹³Csoil values.（3）With the graze intensity increasing,the variation trends of δ¹³Cleaf,δ¹³Croot andδ¹³Csoil were declined.But the δ¹³Croot value showed a trend of increasing first and then decreasing.The δ¹³Croot value riched down along the plant axis:δ¹³Csoil ＞δ¹³Croot＞δ¹³Cleaf.（4）The values of δ¹³Cleaf,δ¹³Croot and δ¹³Csoil showed a regular variation trends with the elevation gradient.The δ¹³Croot and δ¹³Csoil values showed a significant regression relationship with geographical factors before and after grazing.（5）The difference gap between δ¹³Croot and δ¹³Csoil at OG and NG plots（△r-sOG,△r-sNG）.showed significant linear correlation.