title: Effects of drought and changes in vapour pressure deficit on water relations of Populus deltoides growing in ambient and elevated CO2.
abstract: The means by which growth CO(2) concentration ([CO(2)]) affects anatomy and water relations responses to drought and vapour pressure deficit (VPD) were studied for yearly coppiced, 4-year-old Populus deltoides clones that were grown in either 400 mumol mol(-1) (ambient) or 800 mumol mol(-1) (elevated) CO(2) for 3 years. It was hypothesized that, during drought, trees growing in elevated [CO(2)] would have a lower volume flux density of water (J(V)), stomatal conductance (g(s)) and transpiration per leaf area (E), as well as a lower stomatal density and a greater stomatal response to drought and changes in VPD than would trees in ambient [CO(2)]. Trees in elevated [CO(2)] actually had higher J(V) values throughout the study, but did not differ from trees in ambient [CO(2)] with respect to g(s) or E under saturating light or E scaled from J(V) (E(scaled)), all of which indicates that the higher J(V) in elevated [CO(2)] resulted from those trees having greater leaf area and not from differences in g(s). Furthermore, although plants in elevated [CO(2)] had greater absolute leaf loss during the drought, the percentage of leaf area lost was similar to that of trees in ambient [CO(2)]. g(s) and E under saturating light were affected by changes in VPD after the first 9 days of the experiment, which coincided with a large decrease in water potential at a soil depth of 0.1 m. Trees in elevated [CO(2)] had a greater stomatal density and a lower wood density than trees in ambient [CO(2)], both traits that may make the trees more susceptible to xylem cavitation in severe drought. Drought and VPD effects for the P. deltoides clone were not ameliorated by long-term growth in elevated [CO(2)] compared with ambient [CO(2)], and plants in elevated [CO(2)] possessed anatomical traits that may result in greater stress associated with long-term drought.
authors.affiliation: Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA. egbobich@csupomona.edu
authors.forename: Edward G
authors.initials: EG
authors.lastname: Bobich
authors.forename: Greg A
authors.initials: GA
authors.lastname: Barron-Gafford
authors.forename: Katherine G
authors.initials: KG
authors.lastname: Rascher
authors.forename: Ramesh
authors.initials: R
authors.lastname: Murthy
mesh_terms: D002245:Carbon Dioxide / Q000494:pharmacology*; D055864:Droughts; D004777:Environment; D018515:Plant Leaves; D032107:Populus / Q000187:drug effects / Q000502:physiology*; D012987:Soil; D055548:Vapor Pressure; D014867:Water / Q000378:metabolism*; D014934:Wood / Q000502:physiology
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide