Dynamic Effects Of Grazing On Stable Carbon And Nitrogen Isotopes In Leaves Of 10 Species In Desert Steppe

There are apparent changes in the material composition of plants during growth and development,a few studies concentrate on the changes in the stable isotope composition(δ¹³C).The application of stable isotope technology has gradually matured.Plant isotope studies have mostly focused on the correlation between the change ofδ¹³C in woody plant leaves and the environment,and relatively few studies have involved herbaceous plants especially in desert steppe.This study analyzed the carbon and nitrogen isotopes of 10 species in the desert steppe,and explored the grazing pressure effects on the isotope changes during the growing season,in order to providing a microscopic index basis for understanding the physiology and biochemistry of the desert steppe plants.The results were shown as follows:1.The seasonal trends of stable carbon isotope in main plants were as follows:δ¹³C of Stipa krylovii and Kochia sieversii showed a unimodal trend that maximum values occurred in summer;δ¹³C of Agropyron cristatum,Potentilla fruticosa,Leymus chinensis and Cryptosporidium hispida showed a trend of first decreasing and then increasing;δ¹³C of Stipa breviflora,Artemisia frigida,Melilotus ruthenica and Allium tenuifolia decreasing with the growing season.2.Responses of plant leafδ¹³C to grazing intensity.In July,Under light grazing（LG）and heavy grazing（HG）treatments,theδ¹³C of Cryptosporidium hispida leaf was significantly increased（p<0.05）,while the changes of other plants were not significant（p>0.05）.In August,δ¹³C of wheatgrass leaves increased significantly under LG and HG treatments（p<0.05）,and theδ¹³C of Kochia sieversii leaves significantly decreased under LG treatments（p<0.05）,and There were no significant difference under different grazing intensities for other plants（p>0.05）,In September,theδ¹³C of Stipa breviflora leaves decreased significantly（p<0.05）,and theδ¹³C of Kochia sieversii leaves increased significantly（p<0.05）,while the rest of the plants were not significant under HG treatment（p>0.05）.In October,theδ¹³C of the leaves of Stipa breviflora and Allium tenuifolia significantly increased under the LG treatment（p<0.05）.Theδ¹³C of the leaves of Cryptocarya scabra significantly decreased Under the LG and HG treatments（p<0.05）.3.Under different grazing intensity treatments,the change trend of total N content in the leaves of main plants is the same,showing a continuous decreasing trend.The content of total N in leaves of main plants was increased by grazing.Under the treatment of NG,the seasonal variation trend of plant leafδ¹⁵N value and total nitrogen content is firstly decreasing,then increasing and then decreasing.Under the treatment of LG,the leafδ¹⁵N value and total nitrogen content showed a declining trend.Theδ¹⁵N value of plant leaves increased first and then decreased,under the treatment of HG.Light grazing made theδ¹⁵N value of Kochia scoparia and lentil leaves negative,and heavy grazing made theδ¹⁵N value of plant leaves positive.