Indirect drivers of plant diversity-productivity relationship in semiarid sandy grasslands

摘要

Although patterns between plant diversity and ecosystem productivity have been much studied, a consis-tent relationship has not yet emerged. Differing patterns be-tween plant diversity and productivity have been observed in response to spatial variability of environmental factors and vegetation composition. In this study, we measured vegeta-tion cover, plant diversity, productivity, soil properties and site characteristics along an environmental gradient (mobile dune, semi-fixed dune, fixed dune, dry meadow, wet meadow and flood plain grasslands) of natural sandy grasslands in semiarid areas of northern China. We used multivariate anal-ysis to examine the relationships between environmental fac-tors, vegetation composition, plant diversity and productiv-ity. We found a positive correlation between plant diversity and productivity. Vegetation composition aggregated by the ordination technique of non-metric multidimensional scaling had also a significantly positive correlation with plant diver-sity and productivity. Environmental gradients in relation to soil and topography affected the distribution patterns of vege-tation composition, species diversity and productivity. How-ever, environmental gradients were a better determinant of vegetation composition and productivity than of plant diver-sity. Structural equation modeling suggested that environ-mental factors determine vegetation composition, which in turn independently drives both plant diversity and produc-tivity. Thus, the positive correlation between plant diversity and productivity is indirectly driven by vegetation composi-tion, which is determined by environmental gradients in soil and topography.