HR: 16:00h
AN: B54B-01    [Abstracts]
TI: Warming and Carbon Dioxide Enrichment Alter Plant Production and Ecosystem gas Exchange in a Semi-Arid Grassland Through Direct Responses to Global Change Factors and Indirect Effects on Water Relations
AU: * Morgan, J A
EM: jack.morgan@ars.usda.gov
AF: USDA-ARS Rangeland Resources Research Unit, Crops Research Lab 1701 Centre Ave., Fort Collins, CO 80526, United States
AU: Pendall, E
EM: pendall@uwyo.edu
AF: Department of Botany, 1000 E. University Avenue University of Wyoming, Laramie, WY 82071, United States
AU: Williams, D G
EM: dgw@uwyo.edu
AF: Department of Renewable Resources, University of Wyoming, Laramie, WY 82071, United States
AU: Bachman, S
EM: sbachman@uwyo.edu
AF: Department of Botany, 1000 E. University Avenue University of Wyoming, Laramie, WY 82071, United States
AU: Dijkstra, F A
EM: feike.dijkstra@ars.usda.gov
AF: USDA-ARS Rangeland Resources Research Unit, Crops Research Lab 1701 Centre Ave., Fort Collins, CO 80526, United States
AU: LeCain, D R
EM: daniel.lecain@ars.usda.gov
AF: USDA-ARS Rangeland Resources Research Unit, Crops Research Lab 1701 Centre Ave., Fort Collins, CO 80526, United States
AU: Follett, R
EM: ronald.follett@ars.usda.gov
AF: USDA-ARS Soil Plant Nutrient Research Unit, 2150 Centre Avenue Building D, Fort Collins, CO 80526, United States
AB: The Prairie Heating and CO₂ Enrichment (PHACE) experiment was initiated in Spring, 2007 to evaluate the combined effects of warming and elevated CO₂ on a northern mixed-grass prairie. Thirty 3-m diameter circular experimental plots were installed in Spring, 2006 at the USDA-ARS High Plains Grasslands Research Station, just west of Cheyenne, WY, USA. Twenty plots were assigned to a two-level factorial combination of two CO₂ concentrations (present ambient, 380 ppmV; and elevated, 600 ppmV), and two levels of temperature (present ambient; and elevated temperature, 1.5/3.0 C warmer day/night), with five replications for each treatment. Five of the ten remaining plots were subjected to either frequent, small water additions throughout the growing season, and the other five to a deep watering once or twice during the growing season. The watering treatments were imposed to simulate hypothesized water savings in the CO₂-enriched plots, and to contrast the influence of variable water dynamics on ecosystem processes. Carbon dioxide enrichment of the ten CO₂- enriched plots is accomplished with Free Air CO₂ Enrichment (FACE) technology and occurs during daylight hours of the mid-April – October growing season. Warming is done year-round with circularly-arranged ceramic heater arrays positioned above the ring perimeters, and with temperature feed-backs to control day/night canopy surface temperatures. Carbon dioxide enrichment began in Spring, 2006, and warming was added in Spring, 2007. Results from the first year of CO₂ enrichment (2006) confirmed earlier reports that CO₂ increases productivity in semi-arid grasslands (21% increase in peak seasonal above ground biomass for plants grown under elevated CO₂ compared to non-enriched controls), and that the response was related to CO₂- induced water savings. Growth at elevated CO₂ reduced leaf carbon isotope discrimination and N concentrations in plants compared to results obtained in control plots, but the magnitude of changes were highly species specific. Ecosystem-level gas exchange measurements indicated that interactions between watering and CO₂ enrichment increased C cycling over a range of soil moisture conditions, although watering had a greater relative impact on C fluxes than CO₂ enrichment. Results from the combined warming and CO₂ enrichment experiment in 2007 indicate soil fluxes of CO₂ increased with elevated CO₂ and warming, but decreased with warming later in the year compared to un-heated controls. Soil CH₄ uptake was enhanced by elevated CO₂ but reduced by warming, particularly later in the year. Soil fluxes of N₂O were unaffected by treatment. These preliminary results indicate potentially strong feedbacks between carbon cycling and warming are mediated by ecosystem processes in this semiarid rangeland.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1630 Impacts of global change (1225)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting