Grazing And Precipitation Stable Isotope Effect On The Stability Of Typocal Steppe

Recent year, the stable isotope technique is one of the new researching ecological processes approaches and it has rapid and accurate detection characteristics. We researched difference of stable isotope nature abundance, correlation and the changes of stable isotope and elements in different disturbing process of six pasture species in typical steppe in different grazing intensity and precipitation disturbing. The results show that:1. In the state of non-interference, the leaf nitrogen content of C3plants is higher than it in C4plants, it shows that the growing ability of C3plants is better than C4plants. However, the value of δ15N, water use efficiency (WUE), nitrogen utilization of C4plants are higher than C3plants and it shows that tolerance of C4plants is better than C3plants. Grass species> forbs, it displays that grass species is superiority in dry matter accumulation ability and it also has stronger competitiveness.2. After plants experienced grazing disturbance, the leaf nitrogen content of six pasture species shows upward trend with the increasing of grazing intensity. However the value of δ13C in C3plants and C4plants displays different tendency. The value of δ13C in C3plants will decline when the leaf nitrogen content increases but the change is converse in C4plants. The nitrogen utilization of C3plants and C4plants shows downward trend. The leaf carbon content of C3plants keeps basically stable,it declines in C4plants. They show that C3plants strengthen the growth after experience grazing disturbance and display adventurism features but C4plants enhance tolerance and show conservatism features.3. After experience precipitation interference, C3plants and C4plants displays different countermeasure. Water use efficiency (WUE) of C3plants and C4plants don’t show notable changes.Nitrogen use efficiency (NUE) of C3plants don’t have conspicuous change but C4plants decline. The leaf carbon content of C3plants decline but it in C4plants rise. The results show that the dry matter accumulation ability of C4plants is better than C3plants under rich moisture conditions, at the same time C4plants reduce tolerance. The ability of resource use and dry matter accumulation of C3plants don’t show notable changes and C3plants is more inclined to steady growth.4.The results of correlation analysis of plants stable isotope show that:the correlation of leaf nitrogen content and the value of δ13C among six pasture species shows that3kinds of C3plants show negative correlation but3kinds of C4plants display positive correlation. This result illustrates that water use efficiency (WUE) of C3plants will reduce and water use efficiency (WUE) of C4plants will rise when the plant growth capacity increases. The value of C/N in six pasture species will decline with the leaf nitrogen content rising. It shows that the plants have ability to regulate their own element to use when the element content is adequate. The correlation between heavy isotopes δ13C and δ15N has different performance in C3plants and C4plants. C3plants show negative correlation and the correlation is more obvious. It shows that water use efficiency (WUE) and environmental nitrogen resource capacity show negative correlation. When the environmental nitrogen resource is sufficient, water use efficiency (WUE) of C3plants will decline. C4plants don’t display significant correlation. It is because the value of δ13C in C4plants don’t have apparent partition phenomenon.