Influence of grazing pressure on the carbon isotope composition of the grasslands of China: Spatio-temporal variations at multiple scales

我们之前对年龄不同的大量植被、土壤和羊毛的分析表明，在大约一个地区。面积500×300平方公里在1960年代和1990年代发生重大社会经济变化后不久，C4的丰度就增加了。这造成了一个明显的空间结构，C4丰度增加，特别是在大城市周围100公里范围内，随着距离城市的增加，C4丰度呈指数下降。该建议将(I)继续和扩展我们过去对羊毛(+粪便)样本的工作，但将其扩展到林分尺度、锡林流域尺度和国家尺度，以及(Ii)它将有助于通过分析植被来机械地理解所观察到的现象。它符合MAGIM第二阶段分析干旱梯度、放牧梯度和地形梯度的意图。它将主要检验目前的C4丰度是由两个相反的趋势造成的假设：空气中二氧化碳浓度增加导致的减少和过度放牧造成的增加。过度放牧是(地区不同的)社会经济条件造成的。因此，这两种趋势都造成了C4丰度下降或增加的地区的复杂格局。过度放牧影响C3/C4竞争的一个主要影响是它改变了植被的供水。

Our previous analyses of bulk vegetation, soil and wool differing in age have shown that in an area approx. 500 x 300 km² in size the C4 abundance increased shortly after major socio-economic changes in the 1960s and 1990s. This created a pronounced spatial structure with an increased C4 abundance especially within a circle of 100 km around large cities exponentially decreasing with increasing distance to the city. The proposal will (i) continue and extend our past work on wool (+ feces) samples but extend it to the stand scale, the Xilin catchment scale and the country scale and (ii) it will contribute to a mechanistic understanding of the observed phenomena by analyzing vegetation. It fits to the intention of the second phase of MAGIM to analyze aridity gradients, grazing gradients and topographical gradients. It will mainly examine the hypotheses that the present C4 abundance results from two opposing trends: a decrease caused by the increasing CO2 concentration in air and an increase caused by overgrazing. Overgrazing results from (regional differing) socio-economic conditions. Both trends thus create a complex pattern of regions with decreasing or increasing C4 abundance. A main effect of overgrazing influencing the C3/C4 competition is that it changes the water supply of the vegetation.