Collaborative Research: Density dependent plant-mycorrhizal-soil interactions create self-reinforcing feedbacks on woody encroachment in tundra ecosystems

In terrestrial plant communities, woody plants are overtaking their herbaceous (non-woody) relatives. This is happening in plant communities globaly. In tundra ecosystems, the environmental causes of this have been studied extensively, but less is known about the potential influence of biologically-influenced interactions on woody plant abundance and growth rates. This project evaluates the extent to which associations between plants and root-soil fungi contribute to shrub expansion in alpine tundra. Studies will take place at the Niwot Ridge Long-Term Ecological Research (LTER) site. This project integrates field and modeling experiments across different spatial scales to understand plant-soil feedbacks that may result in shrub expansion into alpine ecosystems. This project will engage K-12 students and educators in partnership with "CU Science Discovery" at the University of Colorado, train undergraduate students through project-based research, mentor and train a graduate student on the practice and science of running ecosystem-scale simulations using computers. This project will investigate the role of mycorrhizal associations in shaping density-dependent threshold dynamics and how these feedbacks shift across topographically heterogeneous terrain. The main objectives include (1) quantifying heterogeneity in rates of woody plant expansion using remote sensing and supervised image classification, (2) assessing biotic and abiotic drivers of woody expansion, including mycorrhizal colonization rates, communities, and soil biogeochemistry by pairing remote sensing analysis with field surveys, (3) investigating the role of mycorrhizal symbionts in mediating shrub growth rates and gross nitrogen transformations by transplanting individual shrubs with known mycorrhizal symbionts across a shrub density, and (4) integrating field surveys and experiments into modeling experiments to quantify changes in shrub growth and expansion rates under future scenarios of environmental change, and examine how density-dependent feedbacks shift across topographically complex alpine landscapes. 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.