title: Photosynthetic responses of two eucalypts to industrial-age changes in atmospheric [CO2] and temperature.
abstract: The unabated rise in atmospheric [CO(2)] is associated with increased air temperature. Yet, few CO(2)-enrichment studies have considered pre-industrial [CO(2)] or warming. Consequently, we quantified the interactive effects of growth [CO(2)] and temperature on photosynthesis of faster-growing Eucalyptus saligna and slower-growing E. sideroxylon. Well-watered and -fertilized tree seedlings were grown in a glasshouse at three atmospheric [CO(2)] (290, 400, and 650 µL L(-1)), and ambient (26/18 °C, day/night) and high (ambient + 4 °C) air temperature. Despite differences in growth rate, both eucalypts responded similarly to [CO(2)] and temperature treatments with few interactive effects. Light-saturated photosynthesis (A(sat)) and light- and [CO(2)]-saturated photosynthesis (A(max) ) increased by ∼ 50% and ∼ 10%, respectively, with each step-increase in growth [CO(2)], underpinned by a corresponding 6-11% up-regulation of maximal electron transport rate (J(max)). Maximal carboxylation rate (V(cmax)) was not affected by growth [CO(2)]. Thermal photosynthetic acclimation occurred such that A(sat) and A(max) were similar in ambient- and high-temperature-grown plants. At high temperature, the thermal optimum of A(sat) increased by 2-7 °C across [CO(2)] treatments. These results are the first to suggest that photosynthesis of well-watered and -fertilized eucalypt seedlings will remain strongly responsive to increasing atmospheric [CO(2)] in a future, warmer climate.
authors.affiliation: Centre for Plants and the Environment, University of Western Sydney, Richmond, NSW 2753, Australia. o.ghannoum@uws.edu.au
authors.forename: Oula
authors.initials: O
authors.lastname: Ghannoum
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Phillips
authors.forename: Marie A
authors.initials: MA
authors.lastname: Sears
authors.forename: Barry A
authors.initials: BA
authors.lastname: Logan
authors.forename: James D
authors.initials: JD
authors.lastname: Lewis
authors.forename: Jann P
authors.initials: JP
authors.lastname: Conroy
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
mesh_terms: D001272:Atmosphere; D002245:Carbon Dioxide / Q000378:metabolism*; D005052:Eucalyptus / Q000254:growth & development / Q000378:metabolism*; D006358:Hot Temperature; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D054046:Plant Stomata / Q000378:metabolism; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen