title: Panicum milioides (C(3)-C(4)) does not have improved water or nitrogen economies relative to C(3) and C(4) congeners exposed to industrial-age climate change.
abstract: The physiological implications of C(3)-C(4) photosynthesis were investigated using closely related Panicum species exposed to industrial-age climate change. Panicum bisulcatum (C(3)), P. milioides (C(3)-C(4)), and P. coloratum (C(4)) were grown in a glasshouse at three CO(2) concentrations ([CO(2)]: 280, 400, and 650 μl l(-1)) and two air temperatures [ambient (27/19 °C day/night) and ambient + 4 °C] for 12 weeks. Under current ambient [CO(2)] and temperature, the C(3)-C(4) species had higher photosynthetic rates and lower stomatal limitation and electron cost of photosynthesis relative to the C(3) species. These photosynthetic advantages did not improve leaf- or plant-level water (WUE) or nitrogen (NUE) use efficiencies of the C(3)-C(4) relative to the C(3) Panicum species. In contrast, the C(4) species had higher photosynthetic rates and WUE but similar NUE to the C(3) species. Increasing [CO(2)] mainly stimulated photosynthesis of the C(3) and C(3)-C(4) species, while high temperature had no or negative effects on photosynthesis of the Panicum species. Under ambient temperature, increasing [CO(2)] enhanced the biomass of the C(3) species only. Under high temperature, increasing [CO(2)] enhanced the biomass of the C(3) and C(3)-C(4) species to the same extent, indicating increased CO(2) limitation in the C(3)-C(4) intermediate at high temperature. Growth [CO(2)] and temperature had complex interactive effects, but did not alter the ranking of key physiological parameters amongst the Panicum species. In conclusion, the ability of C(3)-C(4) intermediate species partially to recycle photorespired CO(2) did not improve WUE or NUE relative to congeneric C(3) or C(4) species grown under varying [CO(2)] and temperature conditions.
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2753, Australia.
authors.forename: Harshini
authors.initials: H
authors.lastname: Pinto
authors.forename: David T
authors.initials: DT
authors.lastname: Tissue
authors.forename: Oula
authors.initials: O
authors.lastname: Ghannoum
mesh_terms: D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D057231:Climate Change; D009584:Nitrogen / Q000378:metabolism*; D008897:Panicum / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D054046:Plant Stomata / Q000378:metabolism; D018526:Plant Transpiration / Q000502:physiology; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water; D002734:Chlorophyll; D002245:Carbon Dioxide; D009584:Nitrogen