Can complementarity in water use help explain diversity-productivity relationships in semi-arid grasslands?

Previous studies reported the positive diversity-productivity relationship could be explained by combinations of species with different rooting distributions and greater legume abundance. However, because plant production is limited by soil water availability in arid areas, we study the positive diversity-productivity relationship of Mongolian semi-arid grasslands and the complementary use of water in these diverse plant communities. Plant species richness influences productivity through different pathways involving root weight and soil water content or legume abundance. We have examined these variables in plant species in a controlled site in Mongolia, determined the significance of these different pathways using path analysis, and performed single linear regression analysis between the significant factors. The results of the path analysis backed the hypothesis that the diversity-productivity relationship was not explained by greater legume abundance but by complementary usage of soil water by the plant communities of the arid grassland. These results were further supported by a significant positive relationship between plant species richness and root weight in shallow soil layers, and a negative relationship between plant species richness and water content or water potential, and root weight and soil water content.