title: Drought responses of two gymnosperm species with contrasting stomatal regulation strategies under elevated [CO2] and temperature.
abstract: Future climate regimes characterized by rising [CO2], rising temperatures and associated droughts may differentially affect tree growth and physiology. However, the interactive effects of these three factors are complex because elevated [CO2] and elevated temperature may generate differential physiological responses during drought. To date, the interactive effects of elevated [CO2] and elevated temperature on drought-induced tree mortality remain poorly understood in gymnosperm species that differ in stomatal regulation strategies. Water relations and carbon dynamics were examined in two species with contrasting stomatal regulation strategies: Pinus radiata D. Don (relatively isohydric gymnosperm; regulating stomata to maintain leaf water potential above critical thresholds) and Callitris rhomboidea R. Br (relatively anisohydric gymnosperm; allowing leaf water potential to decline as the soil dries), to assess response to drought as a function of [CO2] and temperature. Both species were grown in two [CO2] (C(a) (ambient, 400 μl l(-1)) and C(e) (elevated, 640 μl l(-1))) and two temperature (T(a) (ambient) and T(e) (ambient +4 °C)) treatments in a sun-lit glasshouse under well-watered conditions. Drought plants were then exposed to a progressive drought until mortality. Prior to mortality, extensive xylem cavitation occurred in both species, but significant depletion of non-structural carbohydrates was not observed in either species. Te resulted in faster mortality in P. radiata, but it did not modify the time-to-mortality in C. rhomboidea. C(e) did not delay the time-to-mortality in either species under drought or T(e) treatments. In summary, elevated temperature (+4 °C) had greater influence than elevated [CO2] (+240 μl l(-1)) on drought responses of the two studied gymnosperm species, while stomatal regulation strategies did not generally affect the relative contributions of hydraulic failure and carbohydrate depletion to mortality under severe drought.
authors.affiliation: Institute of Ecology and Environmental Science, Nanchang Institute of Technology, Nanchang, Jiangxi 330099, China.
authors.forename: Honglang
authors.initials: H
authors.lastname: Duan
authors.affiliation: CSIRO Land and Water Flagship, Private Bag 12, Hobart, Tasmania 7001, Australia.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: O'Grady
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia.
authors.forename: Remko A
authors.initials: RA
authors.lastname: Duursma
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia.
authors.forename: Brendan
authors.initials: B
authors.lastname: Choat
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia.
authors.forename: Guomin
authors.initials: G
authors.lastname: Huang
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia.
authors.forename: Renee A
authors.initials: RA
authors.lastname: Smith
authors.affiliation: Institute of Ecology and Environmental Science, Nanchang Institute of Technology, Nanchang, Jiangxi 330099, China.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW 2751, Australia d.tissue@uws.edu.au.
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
mesh_terms: D002245:Carbon Dioxide; D032462:Cycadopsida / Q000378:metabolism*; D055864:Droughts; D006358:Hot Temperature; D054046:Plant Stomata / Q000378:metabolism*; D012987:Soil
chemical_list: D012987:Soil; D002245:Carbon Dioxide
keywords: drought mortality; hydraulic failure; non-structural carbohydrates; rising [CO2]; rising temperature; stomatal regulation