黄土高原延河流域不同植被类型下土壤生态化学计量学特征

植被类型对黄土高原土壤质量的改善具有重要的作用,而土壤碳、氮、磷生态化学计量比是体现生态系统变化过程的重要依据。研究森林、森林草原、草原植被类型对土壤碳、氮、磷含量及其生态化学计量学特征的影响,对于深入认识黄土高原植被恢复对土壤质量的改良、完善生态化学计量学理论和准确评价植被恢复的生态环境效益具有重要的现实意义。延河流域是黄河的一级支流,自然环境脆弱,植被破坏和土壤侵蚀严重,因此,论文选取延河流域为研究对象,分析不同植被类型对土壤碳、氮、磷养分和生态化学计量学特征的影响。结果表明：3种植被带下,表层土壤有机碳、全氮含量显著高于下层土壤,森林带>森林草原带>草原带;森林草原带、草原带下土壤全磷含量在两层土壤中差异不显著,森林植被对土壤碳、氮、磷具有显著的累积作用,对于提高土壤碳、氮、磷含量具有重要的意义。土壤C∶N在3种植被带下较为稳定,土壤有机碳与全氮存在极显著的正相关关系（P<0.01）;土壤C∶P、N∶P受植被类型的影响较大,森林带显著高于森林草原带和草原带,土壤C∶P、N∶P和C∶N之间存在极显著的正相关关系（P<0.01）。总体来说,植被恢复对土壤质量的改善作用明显,森林植被对该区土壤碳、氮、磷等养分含量的累积作用较好,森林植被具有较大的N∶P,其植被生长主要受P含量的限制;草原植被与森林草原植被N∶P比较低,其植被生长主要受N含量的限制。

Ecological Stoichiometry of Soils in the Yanhe Watershed in the Loess Plateau: The Influence of Different Vegetation Zones

The Loess Plateau in China is one of the most eroded areas in the world. Accordingly, the “Grain-for-Green Program” was implemented on a large scale by the central government from 1999; vegetation restoration has been implemented in this area to remedy the soil degradation problem. Vegetation type plays an essential role in ecosystem recovery and affects soil quality, especially soil carbon (C), nitrogen (N) and phosphorus (P) contents. Nutrient stoichiometry has been successfully used to indicate community succession and vegetation restoration in recent years. Studies on the effects of different vegetation types on soil C, N and P stoichiometry are helpful to understand the relationships between vegetation restoration and soil quality, and also beneficial to understand the processes and functions of the ecological system. The Yanhe River is a tributary of the Yellow River and the Yanhe watershed has fragile ecological environment, limited vegetation and serious soil erosion. We chose the Yanhe watershed as the subject of this study because there are different vegetation zones in the watershed, including trees, shrubs, grasses and different combinations of the three types of vegetation. The effects of vegetation (Forest, Forest-Grass, and Grass zones) on soil C, N, and P stoichiometry in Yanhe watershed were studied in this paper. Soil and vegetation were surveyed in 115 sample sites from 9 watersheds, with 24 sample sites in the Forest zones, 58 sample sites in the Forest-Grass zones and 33 sample sites in the Grass zones. We collected soils at the 0-10 and 10-20 cm soil layers, and analyzed total organic C, total N and total P of the soil. The results showed that type of vegetation had significant effects on soil properties. And soil total nutrients changed with the depth. Soil organic C and total N were higher in the 0-10 cm soil depth than in the 10-20 cm depth in Forest, Forest-Grass, and Grass zones. Soil organic C and total N decreased in the following order: Forest zones > Forest-Grass zones>Grass zones. There were no significant differences in soil organic C and total N content in Forest-Grass and Grass zones. Soil total P did not change significantly among different vegetation types or in the soil profile, ranging from 0.58 to 0.69 g/kg in the 0-10 cm soil layer and from 0.57 to 0.65 g/kg in the 10-20 cm soil layer. Soil C∶N ratios in the 0-10 and 10-20 cm soil layers remained stable, ranging from 9.57 to 12.68 and 9.40 to 11.42, respectively. Soil C∶P ratios varied substantially in both soil layers, with coefficients of variation of 90.95% and 79.41% for the 0-10 cm and 10-20 cm soil layers, respectively. Soil N∶P ratios varied similarly to the soil C∶P ratios. The soil C∶N ratio, which was positively related to soil organic C and total N, was stable in the three vegetation zones. Vegetation type had significant impacts on soil C∶P and N∶P ratios. Soil C∶P and N∶P ratios in the Forest zones were significantly higher than those in the Forest-Grass and Grass zones. Soil C∶N ratio was significantly correlated with the C∶P and N∶P ratios (P>0.01). Overall, vegetation restoration improved soil properties, and the Forest zones were better than the Grass zones for improving soil properties in the Loess Plateau. Vegetation restoration was a suitable and effective method to solve soil degradation problems in the Loess Plateau.