Collaborative Research: The role of belowground resource partitioning in tree biodiversity-ecosystem function relationships

Forests provide many important functions, such as producing timber, retaining nutrients, cooling the air and soil, and providing habitat for wildlife. One factor influencing forest productivity is the number of tree species. In general, forests with more tree species tend to be more productive. While there are some indications that this might be due to belowground resource partitioning, it has been difficult to obtain accurate measurements of these processes. This project investigates whether and how tree roots, including their structure, traits, and microbial partners, drive more efficient sharing of water and nutrients in mixed species forests compared to monocultures. Understanding these mechanisms is critical for predicting the future of forests and for designing effective reforestation strategies. The project invests in STEM workforce training through training of undergraduate interns, graduate students, and a postdoctoral researcher, and engages the public through interpretive exhibits, K-12 curriculum development in partnership with Smithsonian Learning Lab, and a workshop for forest restoration practitioners. This project tests the hypothesis that higher tree species richness increases belowground biodiversity, which in turn promotes complementary resource use and enhances forest ecosystem function. Researchers will leverage North America's longest-running, large-scale forest biodiversity experiment to directly measure belowground resource partitioning rather than inferring it. The project deploys three complementary methodological approaches: (1) state-of-the-art belowground imaging tools such as ground-penetrating radar to map root distributions; (2) isotopic tracers of water and nitrogen to quantify differential resource uptake; and (3) detailed root morphological trait measurements and genetic identification of mycorrhizal fungi. Together, these approaches develop a mechanistic understanding of belowground processes, contributing to basic theories in biological science. Ultimately, the project produces a synthetic evaluation of how belowground complementarity links to aboveground and belowground forest productivity, soil function, and nitrogen retention. This project advances NSF’s priorities in Biotechnology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.