Effects of vegetation blanket cover on the ecological stoichiometry and enzymatic activity of opencast coal mine soils in arid areas

This study aims to explore the effects of different vegetation blanket covers on the nutrient and enzyme activities of open-pit coal mine soils in arid areas. The research object was taken as the Dafeng mine in Ningxia Helan Mountains Nature Reserve. Three vegetation blanket covers were set as straw, straw-coir, and coir. Some parameters were measured, including the organic carbon, total nitrogen, total phosphorus, urease, protease, and alkaline phosphatase, as well as the peroxidase and ecological stoichiometric ratios of the mine soils. The results showed that: 1) The vegetation blanket covered with different materials increased the organic carbon and total nitrogen content of the surface layer of the soil. Specifically, the maximum content was achieved in the soil covered by the coir vegetation blanket. By contrast, there was no significant change in the total phosphorus content, and the organic carbon. Among them, there was the total nitrogen, and total phosphorus content of the soil from 10 to 20 cm. Only the organic carbon content of straw-coir vegetation blanket cover soil decreased with the increasing soil depth in the vertical direction. There was no change in the organic carbon, total nitrogen, and total phosphorus of the rest of the vegetation blanket-covered soil, as the soil depth increased. 2) The vegetation blanket cover with different materials increased C/P and N/P ratios. The maximum was also the soil covered by the coir vegetation blanket. There was no significant change in the C/N. Moreover, there was no change in the C/N, C/P and N/P, as the soil depth increased. 3) The urease and alkaline phosphatase activities of the vegetation blanket-covered soil were significantly higher than those of the bare ground. The soil from 0 to 10cm was greater than that from 10 to 20cm. There was no change in the protease activity with the depth of the soil layer. Furthermore, the catalase activity was significantly higher only in the soil from 0 to 10cm of the coir vegetation blanket than in the soil from 10 to 20 cm. 4) The correlation between soil enzyme activity and environmental factors showed that the total phosphorus of soil and C/N were the main influencing factors to govern the enzyme activity, whereas, the N/P and the total nitrogen of soil were the main factors to drive the enzyme activity. The nutrient content of the soil surface layer increased after the three vegetation blankets were mulched, which also increased the C/P and N/P of the soil surface layer, thus promoting surface soil enzyme activity. In addition, there was a significant positive correlation (P<0.01) among the four enzyme activities. The coir vegetation blanket was more capable to provide soil nutrients, compared with the straw and straw-coir vegetation blankets. The redundancy analysis of soil enzyme activities and environmental factors showed that the total soil phosphorus of soil and C/N were the main influencing factors to govern the enzyme activities, while the N/P and the total nitrogen of soil were the main factors driving the enzyme activities. Consequently, the vegetation blankets cover increased the nutrients in the surface layer of the soil. At the same time, the enzyme activity was also promoted in the surface soil. The findings can provide a strong theoretical basis to implement the ecological restoration of vegetation blankets for the open-pit coal mine soil in arid areas.