title: Long-term growth of soybean at elevated [CO2] does not cause acclimation of stomatal conductance under fully open-air conditions.
abstract: Accurately predicting plant function and global biogeochemical cycles later in this century will be complicated if stomatal conductance (g(s)) acclimates to growth at elevated [CO(2)], in the sense of a long-term alteration of the response of g(s) to [CO(2)], humidity (h) and/or photosynthetic rate (A). If so, photosynthetic and stomatal models will require parameterization at each growth [CO(2)] of interest. Photosynthetic acclimation to long-term growth at elevated [CO(2)] occurs frequently. Acclimation of g(s) has rarely been examined, even though stomatal density commonly changes with growth [CO(2)]. Soybean was grown under field conditions at ambient [CO(2)] (378 micromol mol(-1)) and elevated [CO(2)] (552 micromol mol(-1)) using free-air [CO(2)] enrichment (FACE). This study tested for stomatal acclimation by parameterizing and validating the widely used Ball et al. model (1987, Progress in Photosynthesis Research, vol IV, 221-224) with measurements of leaf gas exchange. The dependence of g(s) on A, h and [CO(2)] at the leaf surface was unaltered by long-term growth at elevated [CO(2)]. This suggests that the commonly observed decrease in g(s) under elevated [CO(2)] is due entirely to the direct instantaneous effect of [CO(2)] on g(s) and that there is no longer-term acclimation of g(s) independent of photosynthetic acclimation. The model accurately predicted g(s) for soybean growing under ambient and elevated [CO(2)] in the field. Model parameters under ambient and elevated [CO(2)] were indistinguishable, demonstrating that stomatal function under ambient and elevated [CO(2)] could be modelled without the need for parameterization at each growth [CO(2)].
authors.affiliation: Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, 1207 West Gregory Drive, Urbana, IL 61801, USA. leakey@life.uiuc.edu
authors.forename: Andrew D B
authors.initials: AD
authors.lastname: Leakey
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Bernacchi
authors.forename: Donald R
authors.initials: DR
authors.lastname: Ort
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Long
mesh_terms: D000064:Acclimatization / Q000187:drug effects*; D002245:Carbon Dioxide / Q000494:pharmacology*; D002940:Circadian Rhythm; D017753:Ecosystem; D010788:Photosynthesis; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism*; D013025:Glycine max / Q000187:drug effects* / Q000378:metabolism*; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide