title: C4 grasses prosper as carbon dioxide eliminates desiccation in warmed semi-arid grassland.
abstract: Global warming is predicted to induce desiccation in many world regions through increases in evaporative demand. Rising CO(2) may counter that trend by improving plant water-use efficiency. However, it is not clear how important this CO(2)-enhanced water use efficiency might be in offsetting warming-induced desiccation because higher CO(2) also leads to higher plant biomass, and therefore greater transpirational surface. Furthermore, although warming is predicted to favour warm-season, C(4) grasses, rising CO(2) should favour C(3), or cool-season plants. Here we show in a semi-arid grassland that elevated CO(2) can completely reverse the desiccating effects of moderate warming. Although enrichment of air to 600 p.p.m.v. CO(2) increased soil water content (SWC), 1.5/3.0 °C day/night warming resulted in desiccation, such that combined CO(2) enrichment and warming had no effect on SWC relative to control plots. As predicted, elevated CO(2) favoured C(3) grasses and enhanced stand productivity, whereas warming favoured C(4) grasses. Combined warming and CO(2) enrichment stimulated above-ground growth of C(4) grasses in 2 of 3 years when soil moisture most limited plant productivity. The results indicate that in a warmer, CO(2)-enriched world, both SWC and productivity in semi-arid grasslands may be higher than previously expected.
authors.affiliation: USDA-ARS, Rangeland Resources Research Unit and Northern Plains Area, Fort Collins, Colorado 80526, USA. jack.morgan@ars.usda.gov
authors.forename: Jack A
authors.initials: JA
authors.lastname: Morgan
authors.forename: Daniel R
authors.initials: DR
authors.lastname: LeCain
authors.forename: Elise
authors.initials: E
authors.lastname: Pendall
authors.forename: Dana M
authors.initials: DM
authors.lastname: Blumenthal
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Kimball
authors.forename: Yolima
authors.initials: Y
authors.lastname: Carrillo
authors.forename: David G
authors.initials: DG
authors.lastname: Williams
authors.forename: Jana
authors.initials: J
authors.lastname: Heisler-White
authors.forename: Feike A
authors.initials: FA
authors.lastname: Dijkstra
authors.forename: Mark
authors.initials: M
authors.lastname: West
mesh_terms: D001272:Atmosphere / Q000737:chemistry; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D003889:Desert Climate; D003890:Desiccation; D017753:Ecosystem; D057232:Global Warming; D010788:Photosynthesis / Q000187:drug effects* / Q000502:physiology; D054046:Plant Stomata / Q000378:metabolism; D018526:Plant Transpiration; D006109:Poaceae / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D012621:Seasons; D012987:Soil / Q000737:chemistry; D014835:Volatilization; D014867:Water / Q000032:analysis; D014959:Wyoming
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide