/AnMtgsAbsts2009.52482 Ecosystem Warming Affects Carbon Dioxide Flux in An Agricultural Soil.

Monday, November 2, 2009: 11:40 AM
Convention Center, Room 326, Third Floor

Gerard Wall1, Richard L. Garcia2, Jean McLain1, Bruce Kimball1, Jeffrey White1 and Michael Ottman3, (1)US Arid-Land Agricultural Research Center, USDA-ARS, Maricopa, AZ
(2)LI-COR, Lincoln, NE
(3)Plant Sciences Department, Univ. of Arizona, Tucson, AZ
Abstract:

Global warming seems likely based on present-day climate predictions. Our objective was to characterize and quantify the interactive effects of ecosystem warming (i.e., canopy temperature, TS), soil moisture content (θS) and microbial biomass (BM: bacteria, fungi) on the intra-row soil CO2 flux (ΦS) of an open-field spring wheat (Triticum aestivum L. cv. Yecora Rojo) crop.  A T-FACE (Temperature Free-Air Controlled Enhancement) apparatus utilizing infrared heaters was employed to elevate values of TS above the wheat crop by 1.5 and 3.0 oC during the diurnal and nocturnal periods, respectively. The experimental design was a completely Randomized Latin Square (2x3) consisting of two levels of TS (i.e., heated, reference with dummy heaters) in three replicates planted on 10 Mar. and 1 Dec. 2008. Values of intra-row ΦS, TS (Model LI-8100, LI-COR, Lincoln, NE) and θS (gravimetrically) were measured from planting until canopy closure. An extraction of soil DNA enabled real-time quantitative polymerase chain reaction of bacterial and fungal markers to estimate BM. Under high θS a 10% increase in ΦS was observed in the heated compared with control plots, and ΦS was positively correlated with an order of magnitude increase in BM.  In contrast, as θS became lower in the heated plots compared with higher θS in the control plots, a 10% reduction in ΦS was observed. Characterization of the response of BM to TS under low θS is ongoing, but preliminary results suggest that ΦS depends on the interactive effects of TS, θS and BM.  Consequently, a more complicated paradigm may be required to elucidate the effect of global climate change on sequestering of C in agricultural soils then previously believed. Knowledge of this interactive effect (i.e., TSxθSxBM) will enable more accurate assessments of the sustainability of cereal crop production in a future high-CO2 world.