|Wall, Gerard - Gary|
Submitted to: ASA-CSSA-SSSA Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2003
Publication Date: 11/1/2003
Citation: Wall, G.W., Kimball, B.A., Ort, D.R., Bernacchi, C.J., Olivieri, L.M., Long, S.P., Harrison, M. 2003. Univariate Effect of Elevated CO2 or O3 On Water Relations of Soybean and Corn Leaves. ASA-CSSA-SSSA Proceedings.
Technical Abstract: Reported herein is the independent univariate effect of either atmospheric CO2 or O3 concentration on upper most sunlit leaf stomatal conductance (gs), transpiration rate (T), total water (1W), osmotic (1") and resultant turgor (1P) potentials, tissue concentration of osmotica (i.e., simple sugars, free amino acids and inorganic ions), and biophysical characteristic of leaf tissue. Soybeans (Glycine max) and corn (Zea maize) plants were exposed to ambient (control; 370 _mol (CO2 ) mol-1; 40-70 nmol (O3) mol-1) and either free-air CO2 (ambient +180 _mol mol-1) or O3 (ambient + 50%) enrichment (FACE) under a typical mid-western (USA) rainfed dryland production system over two growing seasons. Across seasons, leaf surfaces (e.g., adaxial and abaxial) and species during midday (solar noon) elevated CO2 reduced gs by 00 mol (H2O) m-2 s-1 (00%), whereas O3 reduced it by 00 mol (H2O) m-2 s-1 (00%). This resulted in a decreased in T by 00 (00% ) and 00 (00%) mmol (H2O) m-2 s-1 for elevated CO2 and O3, respectively. Compared with control, elevated CO2 increased the concentration of total leaf osmotica and enhanced biophysical characteristics of leaf tissue, whereas O3 had the inverse effect. Elevated CO2 caused more negative (improved) 1W by 0.00 MPa (0%), and caused more negative 1" by 0.00 MPa (0%), thereby, increasing osmotic adjustment resulting in higher values of 1P by 0.00 MPa (0%). Again O3 had only a nominal, or slightly inverse effect as CO2, on 1W, 1" and 1P. Hence, in a future high-CO2 world improved water relations are anticipated in a herbaceous C3 indeterminate dicot such as soybean, and a determinate warm-season C4 monocot grass such as corn. Nevertheless, a concomitant rise in atmospheric O3, along with CO2, will tend to mitigate any ameliorating effect that elevated CO2 will impart on water status. Furthermore, a further rise in atmospheric O3 could have even a more deleterious effect on physiological processes such as water relations in important oil seed (soybean) and grain (corn) crops.