PARENT SESSION
Oral Session # 45: Plant Ecology III: Plant - Water Relations I.
Presiding: R Giuliani
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Carbon dioxide and water vapor exchange in three adjacent ecosystems for two drought-impacted years.

Stoy, Paul^*,1, Katul, Gabriel^{1, 2}, Oren, Ram¹, Siqueira, Mario^{1, 2}, Juang, Jehn-Yih¹, ¹ Nicholas School of the Environment and Earth Sciences, Durham, NC, USA² Department of Civil and Environmental Engineering, Durham, NC, USA

ABSTRACT- Understanding the impacts of vegetation cover on biosphere/atmosphere exchanges of carbon and water is a research priority for ecosystem ecology and management given the close coupling of terrestrial ecosystems and climate. We explored differential impacts of vegetation on CO₂ and H₂O dynamics with two years of eddy-covariance measured CO₂ and H₂O fluxes in three adjacent ecosystems in the Duke Forest, NC: a loblolly pine (Pinus taeda) plantation, an oak-hickory dominated hardwood forest, and a grass field. All three sites experience identical climatic and edaphic conditions. We examined three hypotheses: 1) land cover has a greater impact than environmental drivers on net ecosystem carbon exchange (NEE), 2) environmental drivers have greater impact on evapotranspiration (ET) than land cover, and 3) more diverse ecosystems are more resistant to environmental perturbations. Our primary argument is that H₂O fluxes are primarily controlled by energy supply while CO₂ fluxes are much more dependent on species-specific structure and function, including drought resistance. The carbon and water dynamics of the hardwood forest showed clear functional resistance to mild and severe drought, presenting a management option that is robust to the various environmental perturbations encountered during the measurement period (and for future climate projections for the Southeast). The pine plantation was sensitive to drought and severe weather, but assimilated carbon at a higher rate under drought-free conditions. The grass field represented a net source of CO₂ to the atmosphere during both years of measurement. These results further highlight the dramatic differences in ecosystem function across heterogeneous landscapes, and pose important challenges for understanding ecosystem response to projected global changes.

Key words: evapotranspiration, SE US ecosystems, net ecosystem exchange, eddy-covariance