The role of above- and belowground interactions for plant allocation

My dissertation builds upon decades of research on plant resource allocation, by incorporating multispecies interactions, above- and belowground, with the overarching goal of uncovering the role of a whole community in shaping plant resource allocation and change to subsequent interactions. I accomplished this goal by establishing two controlled common garden experiments where I manipulated the biotic community that a focal plant is exposed to. Using these experiments, 1) I tested whether plant neighbors alter a focal plant’s resource allocation through changes to above- or belowground processes, and if these allocation changes resulted in any indirect effects on the focal plant’s associated community interactions, 2) I examined the three-way relationship between a focal plant, its neighboring plants and its belowground community, with the objective of understanding how biotic context shapes a focal plant’s functional diversity and its interactions with its associated belowground community, 3) I tested whether biotic interactions induce resource allocation growth-defense and growth-reproduction trade-offs in a focal plant. The findings from this dissertation show that focal plant resource allocation and trait variation are significantly affected by the whole community context. Some results were contingent on neighbor identity, such as whether plants are affected by above- versus belowground processes, others showed changes based on conspecific versus heterospecific interactions, regardless of heterospecific neighbor identity. We also provide evidence that changes to allocation and traits can result in growth-reproduction trade-offs based on the biotic context. In a time of exacerbated anthropogenic climate change, biotic interactions are changing at rates and in ways that we have yet to understand. This dissertation advocates for the need to incorporate multispecies interactions into mechanistic models to better understand plant persistence and success with these changing biotic conditions.