Objective By analyzing the changes of soil nutrients and ecostoichiometry in different plantations and varied soil layers in the alpine region of the Loess Plateau, this paper aims to clarify the soil nutrients and stoichiometric characteristics under different plantations, and to reveal the laws of soil nutrients and stoichiometric changes with soil depth.
Method In this paper, plantations (including Picea crassifolia, Larix principis-rupprechtii, Populus cathayana, Betula platyphylla) in the alpine region of the Loess Plateau in Qinghai Province, northwestern China were taken as the research objects, and the grassland of natural conversion and cropland were taken as control. C, N and P contents and stoichiometry ratios of six vegetation types in 0−20 cm, 20−40 cm and 40−60 cm soil layers were determined.
Result (1) The soil C and N contents of different plantations in the alpine region of the Loess Plateau were significantly different (P < 0.05), and the difference of soil P content was partially significant. The C and N contents in each soil layer of plantations were significantly higher than those of grassland and cropland, and the organic carbon and total nitrogen contents in 0−20 cm topsoil of Populus cathayana were the highest, which were 25.82 and 2.17 g/kg, respectively. (2) The soil ecostoichiometry of different plantations in the alpine region of the Loess Plateau was significantly different (P < 0.05). The C∶N of plantations in 0−60 cm soil layer was significantly lower than cropland, while the C∶P and N∶P were higher than those of grassland and cropland (P < 0.05). The ecostoichiometry of Populus cathayana in 0−20 cm topsoil was higher than other plantation types, with C∶N, C∶P and N∶P being 11.99, 43.27 and 3.64, respectively. (3) Correlation analysis showed that the organic carbon in the study area had the closest correlation with total nitrogen (P < 0.01), the total nitrogen had the closest correlation with soil C∶N and N∶P (P < 0.01), and the organic carbon had the closest correlation with soil C∶P (P < 0.01). This indicated that the responses of soil C and N in the study area to different plantations were consistent. The soil C∶N and N∶P were mainly affected by total nitrogen, and the C∶P was mainly affected by organic carbon. (4) In the 0−60 cm soil layer, the soil C, N and P contents of different vegetation types decreased with the increase of soil depth in the alpine region of the Loess Plateau. The soil ecostoichiometry of the vegetation in the study area had no significant changing trend except for Populus cathayana, which decreased with the increase of soil depth. This indicated that plantations had the best improvement effect on the surface soil nutrients.
Conclusion Soil nutrients and ecostoichiometry are significantly different in varied plantations, and the nutrient content and stoichiometry of Populus cathayana in topsoil are the highest. Soil nutrients decrease with the increase of soil depth, while soil ecostoichiometry does not change significantly with soil depth.