College of Soil and Water Conservation, Beijing Forestry University, Beijing, China.
PLoS One. 2020 Nov 5;15(11):e0241859. doi: 10.1371/journal.pone.0241859. eCollection 2020.
The Grain-for-Green project is an important ecological restoration measure to address the degradation of alpine ecosystems in China, which has an important impact on the ecological stoichiometry of soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K). However, soil stoichiometry changes under different vegetation restoration patterns and at different soil depths remain poorly understood in the alpine region of the Loess Plateau. To clarify these soil stoichiometry changes, a 0-60 cm soil profile was sampled from two typical vegetation restoration patterns: grassland (GL) and forestland (FL), including Picea crassifolia (PC), Larix principis-rupprechtii (LR), Populus cathayana (PR) and Betula platyphylla (BP). The control was a wheat field (WF). In all soil layers, the soil organic carbon (SOC), total nitrogen (TN), soil available nitrogen and potassium (AN and AK, respectively) and C:P, C:K, N:P and N:K ratios of FL were higher than those of GL and WF. The TN content and N:P and N:K ratios of GL were higher than those of WF in each soil layer. Additionally, the soil nutrients (except TK) of all vegetation types and stoichiometry of PR and GL (except the N:P ratio of GL) were greater at 0-20 cm than at 20-60 cm. Moreover, the SOC and TN showed the strongest correlation with the soil stoichiometry (except P:K ratio); thus, C and N had the greatest effect on the soil stoichiometry. Furthermore, soil fertility was limited by N. Our results indicated that different vegetation restoration patterns and soil depths had significant effects on the soil nutrients and stoichiometry in the alpine region of the Loess Plateau. The recovery of farmland to forestland promoted better improvements of soil nutrients, and PR had the most significant positive effect on soil surface nutrients.
退耕还林还草工程是中国解决高山生态系统退化的一项重要生态恢复措施，对土壤碳（C）、氮（N）、磷（P）和钾（K）的生态化学计量学有重要影响。然而，黄土高原高山地区不同植被恢复模式和不同土壤深度下的土壤化学计量学变化仍不清楚。为了阐明这些土壤化学计量学变化，在两个典型的植被恢复模式（草地（GL）和林地（FL））和一个农田（WF）中采集了 0-60 cm 的土壤剖面，包括云杉（PC）、落叶松（LR）、杨树（PR）和白桦（BP）。在所有土壤层中，FL 的土壤有机碳（SOC）、总氮（TN）、土壤有效氮和钾（AN 和 AK，分别）以及 C：P、C：K、N：P 和 N：K 比值均高于 GL 和 WF。各土层 GL 的 TN 含量和 N：P 和 N：K 比值均高于 WF。此外，所有植被类型的土壤养分（除 TK 外）和 PR 和 GL 的化学计量（除 GL 的 N：P 比值外）在 0-20 cm 层均大于 20-60 cm 层。此外，SOC 和 TN 与土壤化学计量学（除 P：K 比值外）相关性最强；因此，C 和 N 对土壤化学计量学的影响最大。此外，土壤肥力受 N 限制。我们的结果表明，不同的植被恢复模式和土壤深度对黄土高原高山地区的土壤养分和化学计量学有显著影响。将农田恢复为林地促进了土壤养分的更好改善，而 PR 对土壤表层养分的影响最为显著。
