Assessing Plant-Water Relations in the Face of Climate Change in the Rocky Mountains Using a Turf Transplant Experiment

Alpine communities of the Rocky Mountains show a directional shift in temperature with increasingly hotter and drier growing seasons. In much of the Western United States, climate change models predict an increase in the length and severity of drought during the growing season due to a reduction in precipitation, rise of temperatures, earlier snowmelt dates, and shifts in the North American monsoon. Nonetheless, specific drivers of community composition, function, and ecosystem response are not fully known, but examining functional diversity (FD) will allow us to understand the drivers and how climate change will affect FD.

We hypothesized that climate change will shift vegetation FD. In 2017, we established a novel whole-community turf transplant experiment at three subalpine meadow sites across a 400-meter (spanning a 1.5C change in temperature) elevation gradient near Crested Butte, Colorado. The experimental design allowed us to examine FD before and after the simulated change and if plants respond rapidly to new conditions. By transplanting whole communities into new communities, the experiment also enables us to examine the direct and indirect effects of abiotic change on altered biotic interactions in situ.

We assessed alpine vegetation responses to changes in temperature by measuring water potential (Ψ). Ψ is an important plant hydraulic trait in understanding plant water status in response to resistance to water scarcity. In 2021, we measured ~15 common species along the gradient to assess how cooling and warming temperatures affected predawn and midday Ψ. In 2022, we measured midday Ψ of 5 species that are present across all sites and treatments. For both years, we tested the hypothesis that climate change impacts on vegetation functioning can be modulated by hydraulic buffering of plant Ψs.

Our results show the Ψ of plants in experimental treatments did differ from each other. Increased warming led to more water stress and increased cooling led to less water stress.Warming directly impacts plant physiology and growth via hydraulics and Ψs. Species showed little ability to modulate or acclimate their Ψ responses to temperature. Our results indicate that incorporating Ψ responses to temperature into vegetation models can better link how cooling and warming temperatures affect vegetation functioning.