title: Dominant plant taxa predict plant productivity responses to CO2 enrichment across precipitation and soil gradients.
abstract: The Earth's atmosphere will continue to be enriched with carbon dioxide (CO2) over the coming century. Carbon dioxide enrichment often reduces leaf transpiration, which in water-limited ecosystems may increase soil water content, change species abundances and increase the productivity of plant communities. The effect of increased soil water on community productivity and community change may be greater in ecosystems with lower precipitation, or on coarser-textured soils, but responses are likely absent in deserts. We tested correlations among yearly increases in soil water content, community change and community plant productivity responses to CO2 enrichment in experiments in a mesic grassland with fine- to coarse-textured soils, a semi-arid grassland and a xeric shrubland. We found no correlation between CO2-caused changes in soil water content and changes in biomass of dominant plant taxa or total community aboveground biomass in either grassland type or on any soil in the mesic grassland (P > 0.60). Instead, increases in dominant taxa biomass explained up to 85 % of the increases in total community biomass under CO2 enrichment. The effect of community change on community productivity was stronger in the semi-arid grassland than in the mesic grassland, where community biomass change on one soil was not correlated with the change in either the soil water content or the dominant taxa. No sustained increases in soil water content or community productivity and no change in dominant plant taxa occurred in the xeric shrubland. Thus, community change was a crucial driver of community productivity responses to CO2 enrichment in the grasslands, but effects of soil water change on productivity were not evident in yearly responses to CO2 enrichment. Future research is necessary to isolate and clarify the mechanisms controlling the temporal and spatial variations in the linkages among soil water, community change and plant productivity responses to CO2 enrichment.
authors.affiliation: Grassland, Soil, and Water Laboratory, USDA-ARS, 808 E Blackland Rd., Temple, TX 76502, USA philip.fay@ars.usda.gov.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Fay
authors.affiliation: College of Natural Resources, University of Idaho, PO Box 441133, Moscow, ID 83844, USA Present address: Great Basin Rangelands Research, USDA-ARS, 920 Valley Rd., Reno, NV 89512, USA.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Newingham
authors.affiliation: Grassland, Soil, and Water Laboratory, USDA-ARS, 808 E Blackland Rd., Temple, TX 76502, USA.
authors.forename: H Wayne
authors.initials: HW
authors.lastname: Polley
authors.affiliation: Rangeland Resources Research Unit, USDA-ARS, 1701 Centre Avenue, Fort Collins, CO 80526, USA.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Morgan
authors.affiliation: Rangeland Resources Research Unit, USDA-ARS, 1701 Centre Avenue, Fort Collins, CO 80526, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: LeCain
authors.affiliation: Department of Natural Resources and Environmental Science/MS 186, University of Nevada Reno, 1664 North Virginia, Reno, NV 89557, USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Nowak
authors.affiliation: School of Life Sciences, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, NV 89154, USA.
authors.forename: Stanley D
authors.initials: SD
authors.lastname: Smith
keywords: Central Plains grasslands; Mojave Desert; climate change; community change; primary productivity; rangelands; threshold responses
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