2.2. Plots and treatments
We selected the typical Robinia pseudoacacia as the research object in the loess hilly region, which was the key area for the restoration and reconstruction of ecological environment. In mid-September, 2012, Robinia pseudoacacia with four kinds of stand age (CH10a, CH20a, CH30a, CH40a) and the same soil type (Loessal Soil) were selected in the Zhifanggou watershed. At the same time, slope crop land was selected as the control for explaining the effect of soil different environment on soil carbon flux. The vegetation and topographical features of different plot are shown in Table 1.