Elevated CO2 counteracts effects of water stress on woody rangeland-encroaching species

Authors: O'Connor, Rory; Blumenthal, Dana; OCHELTREE, TROY - Colorado State University; NIPPERT, JESSE - Kansas State University

Submitted to: Tree Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2022
Publication Date: 12/31/2022
Citation: O'Connor, R.C., Blumenthal, D.M., Ocheltree, T.W., Nippert, J.B. 2022. Elevated CO2 counteracts effects of water stress on woody rangeland-encroaching species. Tree Physiology. Article tpac150. https://doi.org/10.1093/treephys/tpac150.
DOI: https://doi.org/10.1093/treephys/tpac150

Interpretive Summary: Woody plants are increasing prevalence and dominance in many rangelands around the world. The reason for their increase is various but two common drivers that have changed are an increase in CO2 concentrations and alteration to precipitation dynamics. We asked what the physiological growth dynamics of four juvenile woody plant species (Cornus drummondii, Rhus glabra, Gleditsia triacanthos and Juniperus osteosperma) when grown in elevated CO2 and chronically water stressed. We found that elevated CO2 counteracts much of the physiological effects of chronic water stress in the four different woody plant species measured. The alleviation of water stress from increased CO2 concentrations will result in juvenile woody plants continuing to expand and establish in North American rangelands. This information will aid land managers in making long-term management objectives for reducing woody plants in rangelands.

Technical Abstract: The ubiquity of woody plant expansion across many rangelands globally has led to the hypothesis that the global rise in atmospheric carbon dioxide concentration ([CO2]) is a global driver facilitating C3 woody plant expansion. Increasing [CO2] also influences precipitation patterns seasonally and across the landscape, which often results in the prevalence of drought in rangelands. To test the potential for [CO2] to facilitate woody plant growth, we conducted a greenhouse study for 150 days to measure CO2 effects on juveniles from four woody species (Cornus drummondii C.A. Mey., Rhus glabra L., Gleditsia triacanthos L., Juniperus osteosperma Torr.) that are actively expanding into rangelands of North America. We assessed chronic water-stress (nested within CO2 treatments) and its interaction with elevated [CO2] (800 p.p.m.) on plant growth physiology for 84 days. We measured leaf-level gas exchange, tissue-specific starch concentrations and biomass. We found that elevated [CO2] increased photosynthetic rates, intrinsic water-use efficiencies and leaf starch concentrations in all woody species but at different rates and concentrations. Elevated [CO2] increased leaf starch levels for C. drummondii, G. triacanthos, J. osteosperma and R. glabra by 90, 39, 68 and 41%, respectively. We also observed that elevated [CO2] ameliorated the physiological effects of chronic water stress for all our juvenile woody species within this study. Elevated [CO2] diminished the impact of water stress on the juvenile plants, potentially alleviating an abiotic limitation to woody plant establishment in rangelands, thus facilitating the expansion of woody plants in the future.