Plant Diversity-Productivity Relationships: An Experimental Evaluation of the Roles of Local Ecological Processes and Species Pool Effects

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Understanding how local and regional processes balance to regulate species diversity is a fundamental goal in ecology. Our research will examine the relative significance of local-scale ecological interactions and species availability in governing relationships between grassland plant diversity, soil nutrient supply, and habitat productivity. We will conduct two factorial field experiments concurrently within a Kansas grassland. In experiment 1, we will directly manipulate soil nutrient supply and plant productivity by applying nitrogen and phosphorus fertilizers to field plots. We will manipulate species availability through the use of multi-species seed additions. In experiment 2, we will manipulate species availability via seed additions in plots arrayed across a natural grassland productivity gradient. With these complimentary approaches, we seek to test a set of predictions regarding: (1) how the pool of available colonists affects the relationship between plant diversity and productivity; (2) how nitrogen and phosphorus supply interact to influence the nature of the diversity-productivity relationship; and (3) how species availability influences rates and pathways of vegetation succession under different conditions of nutrient supply and productivity. We are seeking new insights into the organization of plant communities as well as an enhanced understanding of the processes governing the development of diversity-productivity patterns in grasslands.