The Impact of Genotypic vs. Environmental Variation on Leaf Litter Decomposition in Fremont Cottonwood
Joann Jeplawy1*, Jane Marks2, Thomas Whitham3, and Gerard Allan4, and Rebecca Best5
1School of Earth & Sustainability, Northern Arizona University, Flagstaff, AZ, USA; jrjeplawy@gmail.com
2Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA; jane.marks@nau.edu
3Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA; thomas.whitham@nau.edu
4Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA; gery.allan@nau.edu
5School of Earth & Sustainability, Northern Arizona University, Flagstaff, AZ, USA; rebecca.best@nau.edu
Riparian restoration efforts often focus on foundation species due to their important role in supporting biodiversity, as well as their ability to modulate and stabilize fundamental ecosystem processes such as nutrient cycling. The genotype of a foundation species can affect the survival and abundance of other species, referred to as extended phenotypic effects. For example, studies have shown that intraspecific genetic variation in cottonwoods produces community- and even ecosystem-level effects; however, it is unknown exactly how these extended phenotypes will respond to changed environmental conditions. Because Cottonwood litter forms an important energy link between terrestrial and aquatic systems, we sought to quantify the extent to which variation in aquatic litter decomposition rates is due to genetic vs. environmental effects. We collected litter from Populus fremontii (Fremont cottonwood) growing in common gardens planted across an elevational gradient and placed it in a mid-elevation stream to measure decomposition rates and colonization by aquatic invertebrate communities. We then used linear mixed-effect models to estimate the relative importance of genetic variation vs. environmental effects (litter trait plasticity). We found that litter decomposition was strongly affected by an interaction between population and garden: in other words, litter from the different populations decomposed at different rates depending on the garden in which it was grown. Lab experiments also showed that garden had a large effect on shredding rates by a common aquatic insect. Our results indicate that genotype by environment interactions can have a major influence on the extended phenotypic effects of a foundation riparian tree species, shifting our ability to predict the ecological roles that particular genotypes or source populations will play when planted into new environments.