NSF Award
2310100
Understanding how species interactions affect biological diversity has long been of interest to ecologists. Ecological theory and observations have shown that negative interactions between adult trees and seedlings of the same species stabilize populations, prevent local extinction, and maintain biological diversity. Alternatively, adult trees can increase the growth and survival of younger seedlings of the same species, particularly in stressful environments, which in turn can lead to lower levels of biological diversity. However, the role of pathogens and mutualists in mediating these interactions and giving rise to variation in plant diversity across environmental gradients remains unknown. This research funds a collaboration between plant and fungal population and community ecologists to uncover the role of positive and negative above and below ground plant-microbial interactions in the maintenance of species diversity. It will further explore how changes in environmental stress might impact tree diversity in forest ecosystems. This research will inform and engage local and regional land managers and stakeholders of the role of above and below ground mutualists in the growth and survival of key tree species in the Pacific Northwest.<br/><br/>As the global climate shifts, research into how populations and communities adapt to environmental changes has become increasingly critical. Microbes and their interactions with plants, both positive and negative, play a underexamined role in determining species distributions, abundances, and their expected responses to climate-induced stress. As a result, we lack a comprehensive understanding of how microbially mediated interactions, and in particular above and below ground conspecific feedbacks within and among plant species, change in their strength and direction across environmental stress gradients. The research funded by this award will investigate how fungal symbionts contribute to tree species abundance, distribution, and diversity along stress gradients, both directly and indirectly, by influencing density-dependent interactions and feedbacks among adult and juvenile trees. Researchers will test the hypothesis that the net effect of fungal symbionts on plant performance is correlated with the level of abiotic drought and nutrient stress in the environment, with conspecific feedback shifting from negative to positive as abiotic stress increases. First, in a field experiment at the HJ Andrews Long Term Ecological Research (LTER) site, investigators will reciprocally transplant three focal tree species beneath the canopies of adult conspecific or heterospecific trees along natural moisture and soil-nutrient stress gradients, manipulating fungal mutualists to evaluate their effect on conspecific density-dependent feedback. In greenhouse experiments, trees, microbes, and soil nutrient and drought stress will be manipulated. Finally, this project will integrate host-symbiont dynamics into regional models of forest community dynamics to assess how tree population/community dynamics might be altered under conditions of abiotic stress. Overall, the proposed work will test multiple hypotheses regarding how fungal symbionts contribute to the direction and strength of feedback for dominant tree species in forests of the Pacific Northwest.<br/><br/>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.
