How will climate change affect the physiology, productivity, and fitness of the invasive grass, agrostis capillaris l., in Pacific Northwest prairies?

Background/Question/Methods

Physiology is an important determinant of an organism’s growth and reproduction and will govern a species' ability to persist in a changing climate. Global climate change may alter the structure and function of ecosystems by affecting competitive dynamics between native and invasive species, potentially undermining the effectiveness of current restoration activities. This study examined the roles of water and temperature as drivers of resource-use, productivity, and fitness of the introduced, invasive perennial grass Agrostis capillaris in a manipulative climate experiment conducted in an upland prairie in Oregon’s Willamette Valley.  Plots were restored by using an herbicide application to suppress existing non-native vegetation and then seeding with a suite of native prairie species.  Climate was manipulated by increasing temperature 3 ºC with overhead infrared lamps and increasing precipitation 25% in a full factorial design. This study focused on the plant establishment phase following restoration, an important period that affects which species initially establish dominance. Our objectives were to determine the physiological and morphological traits that best explained the productivity and fitness of the dominant pre-treatment species at the study site, A. capillaris, under the four climate treatments following restoration.

Results/Conclusions

Data on leaf-level fluxes of CO₂ and water vapor, leaf morphology, water potential, plant size, aboveground biomass, percent cover, and fitness were collected in 2010. Leaf gas exchange rates were similar across treatments. While photosynthetic and transpiration rates differed on diurnal and seasonal time scales, diurnal water-use efficiency remained constant. Individuals displayed lower leaf surface area and basal area in precipitation treatments, and greater aboveground biomass in heating treatments. Absolute cover was highest in heated plots, but relative cover as proportion of total vegetation was similar across treatments, suggesting that this species’ relative dominance was not affected by climate manipulation. Results suggest that Agrostis capillaris may invade novel environments by i) maintaining metabolic homeostasis through water-use efficiency rates, and by ii) exhibiting morphological plasticity, as suggested by the production of alternative growth forms in precipitation treatments. In 2011, we are collecting a similar suite of data on A. capillaris and three additional native grass species. During the establishment year, relative cover of native perennial grasses was greater in the heating-only treatment, indicating that native and introduced species may respond differently to climate change.