Stable Carbon And Nitrogen Isotope Analyses On Modern Wheat And Leymussecalimus Of The Northwest China And The Relationship Between Stable Isotope With Climatic Factors

In this study, modern samples of wheat and Leymussecalimus from the Northwest China were taken and the stable carbon and nitrogen isotopes of wheat seeds and Leymussecalimus leaves were tested. The testing results are:1) The δ13C value of 62 samples of wheat seeds varies from -23.14‰ to -27.84‰ with the average value of 25.82‰ in the studied area. The average value deflects positively than the average δ13C value of global C3 plants, and deflects positively than the average 813C value of C3 grass plants throughout the North China and the arid and semi-arid Northwest China.The δ13C value of 29 samples of wheat seeds varies from-29.61‰ to -24.93‰ with the average value of-26.99‰ in the studied area.The mean value nears the average 813C value of global C3 plants,but it is less than the average δ13C value of C3 grass plants throughout the North China and the Northwest China arid and arid and semi-arid Northwest China.2) The δ15N value of 61 samples of wheat seeds varies from-3.65‰ to 9.87‰ with the average value of 2.19‰ and The δ15N value of 29 samples of Leymussecalimus leaves varies from-1.49‰ to 8.11‰ with the average value of 3.19‰ in the studied area.The δ13C value and δ15N value of wheat seeds and Leymussecalimus leaves to the MAT (Mean Annual Temperature)and the MAP (Mean Annual Precipitation)were studied through regressive analysis,so we gained the following conclusions:1) In East of the Yellow River region, the water which is needed for wheat growth mainly comes from the local precipitation, so there is a strong correlation coefficient between the δ13C value of wheat seeds and the MAP. In West of the Yellow River region, the water needed for wheat growth gets additional supplementary coming from the humans, so there is no correlation coefficient between δ13C value of wheat seeds and the MAP.2) The study also shows a positive correlation between the δ13C value of Leymussecalimus leaves and the MAP.This result responses the Leymussecalimus growth is not limited by moisture condition in arid and semi-arid climatic area.3) There are strong correlation coefficients between the δ13C value of wheat seeds and Leymussecalimus leaves and the MAT on quadratic curve in studied area. The δ13C value of wheat seeds were negatively related to the MAT and the δ13C value of wheat seeds occur the minimum value when the MAT was 9.5℃,but the curve of returns does not exist an apparent turning, the δ13 C value of Leymussecalimus leaves also exists a minimum value when the mean temperature was 9.5℃.in addition, the 813C value of Leymussecalimus leaves were negatively related to the MAT when the MAT was less than 9.5℃ and positively related to the MAT when the MAT was more than 9.5℃.4) The mean δ15N value of wheat seeds and Leymussecalimus leaves in arid and semi-arid are more than in Subhumid regions of Loess Platea,but the δ15N value of wheat seeds and Leymussecalimus leaves were not related to the MAT and the MAP in the Study area.