Mechanisms of Coexistence: Implications for Biodiversity-Ecosystem Functioning Relationships in a Changing World

Abstract

Recent advances in the understanding of the effects of biodiversity on ecosystem processes have left unanswered questions on the mechanistic basis of this relationship and how it may change in the face of global climate change. There is a strong theoretical basis connecting species coexistence with the positive effect of biodiversity on productivity (overyielding) and my research program examines two such mechanisms of coexistence and overyielding in grassland communities: belowground spatial resource partitioning by plant species, and plant-soil feedbacks. In chapter 1, I first assessed how plant diversity and warming will directly and interactively affect plant communities in a long-term warming and diversity field experiment. I found that warming and diversity have positive direct effects on plant biomass, and the two factors have positive interactive effects on aboveground biomass while the effect of warming on belowground biomass trends negative at the highest diversity level, and this response may be related to shifting community structure under warmed conditions. In chapter 2, I examined the belowground biomass dynamics and nitrogen supply rates under warming and diversity treatments and the implications of these for plant productivity. My results hint at a potential for a positive feedback between diversity-enhanced deep-soil nitrogen mineralization and increased fine rooting depth that may drive positive effects of warming on plant productivity. In chapter 3, I address whether feedbacks between plants and associated plant species-specific soil biotic communities contribute to the positive effect of diversity on plant productivity. I conclude that while present, plant-soil feedbacks are not the dominant driver of overyielding in our grassland system. By furthering the understanding of drivers of diversity-productivity relationships and how these may be altered under climate change, we allow a more complete, mechanistic understanding of community dynamics, enabling stronger prediction of the consequences of human dominance of the earth.