黄土高原高寒区不同人工林土壤养分及生态化学计量特征

  目的  通过分析黄土高寒区不同人工林和不同土层的土壤养分和生态化学计量变化，旨在阐明不同人工林土壤养分和化学计量特征，揭示土壤养分和化学计量随土层深度的变化规律。  方法  以青海黄土高寒区退耕的人工林地（包括青海云杉、华北落叶松、青杨、白桦）为研究对象，以自然退耕的草地和农田为对照，测定了6种植被类型在0 ~ 20 cm、20 ~ 40 cm和40 ~ 60 cm土壤层的C、N、P含量及生态化学计量比。  结果  （1）黄土高寒区不同人工林的土壤C、N含量差异显著（P < 0.05），P含量部分差异显著；人工林地各土层的C、N含量显著高于草地和农田，且青杨林在0 ~ 20 cm表土层的有机碳、全氮含量最高，分别为25.82、2.17 g/kg。（2）黄土高寒区不同人工林的土壤生态化学计量有显著差异（P < 0.05）；0 ~ 60 cm土层中人工林地的C∶N显著低于农田，C∶P和N∶P高于草地和农田（P < 0.05）；青杨在0 ~ 20 cm表土层的生态化学计量比其他人工林类型高，C∶N、C∶P和N∶P分别为11.99、43.27和3.64。（3）相关性分析表明，研究区土壤的有机碳与全氮相关性最紧密（P < 0.01），全氮与土壤C∶N和N∶P相关性最紧密（P < 0.01），有机碳与土壤C∶P相关性最紧密（P < 0.01）。说明研究区土壤C、N对不同人工林的响应具有一致性，土壤的C∶N和N∶P主要受全氮的影响，C∶P主要受有机碳的影响。（4）在0 ~ 60 cm土层中，黄土高寒区不同植被类型的土壤C、N、P含量均随土壤深度的增加而降低。研究区土壤的生态化学计量除青杨随土壤深度的增加而下降外，其他退耕植被无显著变化趋势。说明人工林对表层土壤养分的改良效果最好。  结论  不同人工林的土壤养分及生态化学计量有显著差异，且青杨林表层土壤的养分含量和化学计量最高；土壤养分随土壤深度的增加而降低，土壤生态化学计量随土壤深度变化不显著。 

Soil nutrients and ecostoichiometric characteristics of different plantations in the alpine region of the Loess Plateau

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 sixvegetation types in 0-20 cm, 20-40 cm and 40-60 cm soil layers were determined. Result] (1) The soil Cand 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 soillayer of plantations were significantly higher than those of grassland and cropland, and the organic carbonand total nitrogen contents in 0-20 cm topsoil of Populus cathayana were the highest, which were 25.82 and2.17 g/kg, respectively. (2) The soil ecostoichiometry of different plantations in the alpine region of theLoess Plateau was significantly different (P < 0.05). The C∶N of plantations in 0-60 cm soil layer wassignificantly 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 plantationtypes, with C∶N, C∶P and N∶P being 11.99, 43.27 and 3.64, respectively. (3) Correlation analysis showedthat the organic carbon in the study area had the closest correlation with total nitrogen (P < 0.01), the totalnitrogen had the closest correlation with soil C∶N and N∶P (P < 0.01), and the organic carbon had the closestcorrelation with soil C∶P (P < 0.01). This indicated that the responses of soil C and N in the study area todifferent plantations were consistent. The soil C∶N and N∶P were mainly affected by total nitrogen, and theC∶P was mainly affected by organic carbon. (4) In the 0-60 cm soil layer, the soil C, N and P contents ofdifferent 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 forPopulus cathayana, which decreased with the increase of soil depth. This indicated that plantations had thebest improvement effect on the surface soil nutrients. Conclusion] Soil nutrients and ecostoichiometry aresignificantly different in varied plantations, and the nutrient content and stoichiometry of Populus cathayanain topsoil are the highest. Soil nutrients decrease with the increase of soil depth, while soil ecostoichiometrydoes not change significantly with soil depth.