乌兰布和沙漠典型灌木群落土壤化学计量特征

乌兰布和沙漠不同典型灌木群落类型对荒漠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。研究不同灌木植被类型对土壤碳、氮、磷含量及其生态化学计量学特征的影响，对于深入认识乌兰布和沙漠典型灌木植被生长与修复对土壤质量的改良，准确评价植被生态环境效益具有重要的现实意义。在乌兰布和沙漠8个主要建群种天然植被类型灌木林地内设置10 m×10 m的标准样方进行调查，在灌丛边缘（东、南、西、北四个方向）进行土壤分层采样，取样深度分别为0-20、20-40、40-60、60-80、80-100 cm，共5层。将相同层次土壤样品充分混合，经四分法取样，风干，过0.15 mm筛用于土壤C、N、P含量的测量，分析不同灌木类型各土层碳、氮、磷含量及其生态化学计量比的垂直分布特征，探寻各指标间的相关关系。结果表明：乌兰布和沙漠地区8种天然灌木林土壤有机C、全N、全P含量整体水平不高，分别为2.45、0.26、0.28 g/kg，均低于全国水平。由C、N、P含量的相关性分析可知三者间呈显著正相关（P < 0.05），且C、N元素含量变化几乎同步，但P元素含量变化滞后于二者。各灌木类型表层（0-20cm）土壤C、N、P含量均较高，各灌木类型土壤有机C、全N含量随着土壤深度的增加呈下降趋势，而不同灌木类型土壤全P含量从上至下分布规律不同，且土层对P含量无显著差异（P > 0.05）。8种典型灌木群落土壤整体C：N、C：P、N：P值（9.41、8.70、0.93）低于全国水平，各灌木类型土壤N：P和C：P随土壤深度而递减，但不同灌木类型土壤C：N随土层深度的变化规律不同。乌兰布和沙漠典型灌木群落土壤碳、氮、磷化学计量特征值均低于全国水平，各灌木类型土壤C、N、N：P和C：P随土壤深度而递减，但不同灌木类型土壤P、C：N随土层深度的变化规律不同。有机C、全N、全P与其化学计量比之间具有非线性耦合关系。C：N和P含量具有较高的稳定性（CV=22.45%和24.39%），C：P和N：P比值是研究区限制性养分判断的重要指标。

Soil stoichiometry in typical shrub communities in the Ulan Buh Desert

Different typical shrub communities have made an important contributions to alleviating the problem of soil degradation in the Ulan Buh Desert. Shrub type plays an essential role in ecosystem recovery and affects soil quality, particularly the contents of carbon (C), nitrogen (N), and phosphorus (P). In recent years, stoichiometry has been successfully used to indicate community succession and vegetation restoration, and studies on the effects of different shrub types on soil C, N, and P stoichiometry have contributed to our understanding of the relationships between vegetation restoration and soil quality, and are also beneficial with regards to determining the processes and functions of ecological systems. In this study, standard sampling plots of 10 m×10 m were established in shrub woodland of Ulan Buh Desert natural vegetation types, and soil stratified sampling was carried out in the marginal sections (east, south, west, and north directions) of plant shrubs, with sampling depths being divided into five layers:0-20, 20-40, 40-60, 60-80, and 80-100 cm. Soil samples collected from the same levels were mixed, dried, and passed through a 0.15 mm sieve, and subsequently analyzed using the four-point method to determine the contents of C, N, and P in soil. The soil organic C, total N, and total P contents in the 0-100 cm layer of soil were measured and ecological stoichiometric characteristics in different shrubs and soil depths were compared. Correlations between indicators were also determined. The results showed that the mean contents of soil C, N, and P were 2.45, 0.26, and 0.28 g/kg, respectively, which were all below the national levels. In all the four soils, there was a moderate variation in the stoichiometric characteristics of C and P, whereas there was a relatively marked variation in soil N. Correlation analysis of the elements showed extremely significant correlations between C and N, C and P (P < 0.01), and N and P (P < 0.05). Furthermore, C and N showed almost synchronous variation, whereas P invariably showed a lag. The contents of soil C, N, and P in the surface layer (0-20 cm) of soil associated with each shrub type were higher than those in deeper soil. The ratios of both soil C and N decreased significantly with increasing soil depth, whereas the vertical pattern of soil P differed from top to bottom. There was no significant difference in the P content of different soil layers (P > 0.05). The mean soil C:N, C:P, and N:P ratios were 9.41, 8.70, and 0.93, respectively, which were all below the national level. Soil C and N contents and N:P and C:P ratios decreased significantly with increasing soil depth, whereas the vertical pattern of soil P and the C:N ratio differed from top to bottom. The soil organic C, total N, and total P and the stoichiometric ratios of the typical shrub community in the Ulan Buh desert were found to have a non-linear coupling relationship. The soil C:N ratio and P content have high stability (CV=22.45% and 24.39%, respectively), whereas the C:P and N:P ratios are important indicators for determining nutrient limitation.