Our nationâ€™s health, prosperity and welfare depends, in part, on the resilience and stability of natural ecosystems and the services they provide. Many of these ecosystems are threatened due to the combined impacts of environmental change and invasion by exotic species. In the American Southwest, which is experiencing record increases in temperature and exotic species disturbance, there is a pressing need to understand whether plants and animals will be able to adapt to a rapidly changing landscape. This project will use the National Ecological Observatory Network (NEON) and data collected with NEON's airborne observational platform to study forested river and stream ecosystems, which are critical for providing clean water, nutrient cycling, natural water flow, agricultural productivity and many recreational activities. Using a combination of experimental gardens composed of thousands of Fremont cottonwood trees, and airborne remote sensing technology, the team will examine the capacity these trees have to tolerate heat stress, drought and habitat disturbance caused by salt cedar, a major invasive plant of the southwestern U.S. They will investigate different strategies which the trees may use to adapt to environmental change including physiological and genetic mechanisms, and through the interactions of their roots with fungi in the soil. The studies will include training opportunities for postdoctoral researchers, graduate and undergraduate students. Results from this project will increase our understanding of how tolerant cottonwood forests are to the combined impacts of environmental change and invasive species. The researchers will also develop an education program for high school students, site tours, workshops and land management strategies that capitalize on these treesâ€™ natural abilities to adapt to rapid environmental change.
Three major hypotheses will be tested: 1) Fremont cottonwood genotypes from warm and cool regions of the species distribution will show differential strategies for regulating leaf temperature and carbon balance as an adaptive response to heat stress; 2) Naturally occurring interspecific hybridization will produce hybrids that are better adapted to both drought and salt cedar invasion; 3) mycorrhizal symbioses associated with cottonwoods will promote survival and adaptation to drought and soils that have been altered by invasive tamarisk. These hypotheses will be integrated from the perspective of phenotypic plasticity - an organismâ€™s response to a changing or novel environment - that is often a primary mechanism of adaptation. Phenotypic plasticity will be evaluated using a combination of greenhouse experiments, established common gardens and remote sensing technology using a NEON hyperspectral/lidar platform. This platform will allow us to scale measurements taken from local, replicated tree genotypes (greenhouse and common gardens) to a landscape scale by critically evaluating tree genotype responses that involve gene, environment and gene x environment interactions that occur across the speciesâ€™ distribution. We will apply the knowledge gained in the common gardens to broad parts of the Southwest and predict, at the canopy scale, which trees may be more susceptible to environmental change. Results are anticipated to provide critical information on key adaptive strategies that riparian foundation trees may use to cope with the combined impacts of temperature increase and exotic speciesâ€™ invasion. Our over-arching goal is to develop solutions to these combined threats using a foundation species that is recognized as being critically important for biodiversity conservation and could serve as a model for adaptive management of arid regions in the Southwestern U.S. and around the world.
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.