Trading water for carbon in the future: Effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland

Authors: MUELLER, KEVIN - Cleveland State University; OCHELTREE, TROY - Colorado State University; Kray, Julie; BUSHEY, JULIE - Colorado State University; Blumenthal, Dana; WILLIAMS, DAVID - University Of Wyoming; PENDALL, ELISE - University Of Western Australia

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2022
Publication Date: 6/25/2023
Citation: Mueller, K., Ocheltree, T., Kray, J.A., Bushey, J., Blumenthal, D.M., Williams, D., Pendall, E. 2023. Trading water for carbon in the future: Effects of elevated CO2 and warming on leaf hydraulic traits in a semiarid grassland. Functional Ecology. Article e16314. https://doi.org/10.1111/gcb.16314.
DOI: https://doi.org/10.1111/gcb.16314

Interpretive Summary: Understanding how plant hydraulic traits, which control the cycling of water and carbon, respond to climate change can help predict future rangeland composition and productivity. In a Wyoming semiarid mixedgrass prairie, we assessed the response of several plant hydraulic traits to elevated concentrations of carbon dioxide (CO2; by ~200 ppm) and warming (by approximately 3 degrees Fahrenheight during the day, approximately 6 degrees at night). Hydraulic traits and climate responses varied widely among the grasses and grasslike plants (blue grama, needleleaf sedge, and western wheatgrass), subshrub (fringed sage) and forb (scarlet globemallow) studied. Under elevated CO2, the grasses and grasslike plants became less drought tolerant (lost turgor more easily). The warm-season grass, blue grama, also displayed lower stomatal area. Among the studied species, cool season grasses and grasslike plants displayed the most flexible drought responses, which may favor these and similar species under future climatic conditions.

Technical Abstract: 1. Plant hydraulic traits control flows of carbon dioxide and water through plants and terrestrial ecosystems. Also, the effects of climate change on plants and ecosystems are likely contingent upon the phenotypes of plant hydraulic traits, including inter-specific and intra-specific variability. Yet, integrative studies of hydraulic traits and climate change are rare. 2. In a semiarid mixedgrass prairie in North America, we assessed the response of several plant hydraulic traits to elevated concentrations of carbon dioxide (CO2; by ~200 ppm) and warming (by 1.5' during the day, 3' at night). For leaves of five species, including three graminoids and two forbs, we measured: stomatal density and size, xylem vessel size, turgor loss point, and water potential (pre-dawn). 3. Interspecific differences in hydraulic traits were larger than intraspecific shifts induced by elevated CO2 and/or warming. Some species showed little plasticity in hydraulic traits, especially the forbs, which likely utilize deeper soil water based on their less negative pre-dawn water potentials. Except for xylem dimensions, effects of elevated CO2 were greater than effects of warming, and interactions between CO2 and warming treatments were weak or not detected. The three graminoids, Bouteloua gracilis, Carex duriuscula, and Pascopyrum smithii, had leaf water potentials and turgor loss points that were 10 to 50% less negative under elevated CO2. The C4 grass B. gracilis also reduced allocation of leaf area to stomata due to elevated CO2. Shifts in hydraulic traits under elevated CO2 appeared to be mostly ‘direct’ (a proximate consequence indicating CO2-effects on leaf physiology), rather than ‘indirect’ (mediated by the higher abundance of soil water in elevated CO2 plots). 4. These results suggest climate change might cause some dominant graminoid species in this extensive grassland to adjust their drought resistance strategy away from tolerance, and perhaps toward avoidance. Integration of our results with others’ indicates that common species in this semiarid grassland are more likely to adjust stomatal aperture in response to near-term climate change, rather than adjusting anatomical hydraulic traits. This conclusion contrasts with apparent effects of changing CO2 on plant anatomy over evolutionary time.