Effects of fencing enclosure and artificial vegetation construction on the stoichiometry characteristics of plant－soil carbon, nitrogen, and phosphorus in northern sandy areas based on Meta-analysis

Fencing enclosure and artificial vegetation construction are two effective restoration measures of degraded grassland ecosystems. These measures are widely used in grassland management in sandy areas of north China. In order to clarify the influence of artificial restoration measures on the stoichiometric characteristics of plant－soil carbon (C), nitrogen (N), and phosphorus (P) in the sandy areas of northern China, we selected 52 related literature for Meta-analysis, and discussed the degraded grassland plants after adopting two recovery measures (fencing enclosure and artificial vegetation construction) for different years (≤ 5 years, 5～15 years, and > 5years). The results showed that both fencing enclosure and artificial vegetation construction can significantly increase organic C, total N, and total P contents in soil (P < 0.05), with the magnitude of increase of these parameters decreasing with increasing soil depth. After enclosure restoration, the total C content of plant leaves and roots increased by 3.26% and 4.72% while the total N and P contents of leaves decreased by 18.41% and 44.54% (P < 0.05), respectively. Furthermore, the organic C and total N contents of soil increased greatly after artificial vegetation construction, especially when the restoration period was more than 15 years, indicating that artificial vegetation construction had a better effect on soil restoration. Under long-term enclosure (> 15 years), the C ꞉ N ratio increased significantly by 38.97% (P < 0.05), indicating that the soil was deficient in N. Surface soil C ꞉ P and N ꞉ P ratios increased significantly by 116.78% and 89.04% (P < 0.05), respectively, at the later stage of artificial vegetation construction, suggesting that the soil might be deficient in P. Both restoration measures could improve soil quality, but the initial soil organic C content was low before soil restoration, and the rate of increase of C content was higher than that of N or P content, indicating N and P deficiency during the late stage of long-term enclosure and artificial vegetation construction, respectively. During the later stage of restoration, N and P elements should be supplemented to the soil to further promote the restoration of degraded grasslands.