PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
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Canopy radiation- and water-use efficiencies of cheatgrass as affected by pulse and gradual N fertilization.
SU, BO*,1, HUI, DAFENG1, VERBURG, PAUL2, OBRIST, DANIEL2, ARNONE, JOHN2, JOHNSON, DALE3, EVANS, R.4, LUO, YIQI1, 1 Department of Botany and Microbiology, Norman, OK2 Desert Research Institute, Reno, NV3 Department of Environmental and Resource Sciences, Reno, NV4 University of Arkansas Stable Isotope Laboratory, Fayetteville, AR
ABSTRACT- Biogeochemical interactions among nitrogen, water, and carbon cycles are crucial in determining ecosystem functions. In this study, we used an environmentally controlled growth facility, EcoCELLs, to directly determine the canopy carbon- and water-fluxes and to investigate the effects of pulse N fertilization (PF) and gradual N fertilization (GF) on canopy radiation- and water-use efficiencies of a model ecosystem with cheatgrass (Bromus tectorum). Our analysis showed that PF enhanced daily carbon-flux and water-flux by up to 19% and 5.2%, respectively, compared with GF during the first-half growing period. But GF resulted in higher carbon-flux and water-flux by about 40% and 8.5%, respectively, than PF in the second-half growing period. Consequently, radiation-use efficiency (RUE) was 6.8% higher in PF than in GF up to 49 days after treatment (DAT) but 23% higher in GF than in PF after 49 DAT until the end of the experiment. Similarly, water-use efficiency (WUE) was 20% higher in PF than in GF up to 55 DAT but 24% higher in GF than in PF after 55 DAT. Both RUE and WUE displayed strong diurnal variations, with RUE being close to minimum at noontime and WUE being highest in middle morning and lowest in late afternoon. This study indicates that different N fertilization regimes change dynamics of canopy carbon and water fluxes differently, resulting in higher seasonal average RUE and WUE in GF than in PF.
KEY WORDS: canopy development, nitrogen fertilization, radiation-use efficiency, water-use efficiency