黄土高原草地土壤水分和物种多样性沿降水梯度的分布格局

研究土壤水分、生物多样性的空间变异性是认识陆地生态系统对降水变化的响应特征及适应机制的有效途径。论文利用黄土高原自东南向西北的天然降水梯度,采用样带研究方法对47个草地0~3 m土壤水分和物种多样性进行测定,系统分析了草地土壤水分和植物物种多样性在降水梯度上（250~550 mm）的空间分异及二者之间的权衡关系。结果表明：降水自东南向西北递减是控制黄土高原草地0~3 m土壤水分和物种多样性空间异质性的关键因素。随降雨减少,土壤水分呈线性递减趋势,其中浅层土壤水分（0~1 m）与年降水量相关系数最大。物种丰富度指数和物种多样性指数随降水减少呈显著的线性递减趋势,物种均匀度指数在降水梯度上没有明显变化。370 mm年均降水量是物种多样性和土壤水分权衡关系的转折点,转折点以上二者存在协同关系,即土壤水分和物种多样性沿降水梯度以相同速率变化。370 mm年均降水量以下,物种多样性和土壤水分的权衡增大,意味着维持物种多样性以消耗土壤水分为代价。

Spatial Variation of Soil Moisture and Species Diversity Patterns along a Precipitation Gradient in the Grasslands of the Loess Plateau

The spatial variations of soil moisture and biodiversity have become central issues in ecohydrology which contribute to the understanding of the response of terrestrial ecosystem to precipitation change in water-limited areas. Based a precipitation gradient (250-550 mm) in the Loess Plateau, vertical soil moisture (0-3 m) and species diversity at 47 grassland sites across a southeast-northwest transect were surveyed. The spatial variations of soil moisture and species diversity were evaluated, and the tradeoff between them along the precipitation gradient was quantified. Results showed great variation of soil moisture in the vertical profiles along the precipitation gradient. Significant linear correlation existed between the average soil moisture of the profile and the mean annual precipitation, and the soil moisture in the shallow layer (0-1 m) was affected more greatly by mean annual precipitation. The Patrick index and Shannon-Wiener diversity index also showed positive linear correlation with precipitation, however, Pielou evenness index did not (P>0.05). The linear piece-wise quantile regression was applied to determine the inflection points of the response of tradeoff between species diversity and soil moisture to the precipitation gradient. It revealed obvious trend of the tradeoff along the precipitation gradient. The inflection point of the tradeoff was detected at the mean annual precipitation of 370 mm. Under the 370 mm annual mean precipitation, soil moisture constrains species diversity in the relatively arid regions, while the synergy between soil moisture and species diversity exists in the relatively humid regions in this study. This suggests species maintaining in the relatively arid regions is at the cost of soil water. The results demonstrate that the precipitation gradient determined the tradeoff between soil moisture and species diversity in the grasslands of the Loess Plateau. Consequently, this tradeoff could be an ecological indicator and tool for restoration management in the Loess Plateau.