PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.

Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Stimulation of GPP by CO₂ enrichment in the Duke Forest FACE Experiment estimated using PnET-Day.

Springer, Clint^*,1, DeLucia, Evan², Thomas, Richard¹, ¹ West Virginia University, Morgantown, WV² University of Illinois at Urbana-Champaign, Urbana, IL

ABSTRACT- The objective of the Duke Forest Free-Air-CO₂-Enrichment (FACE) experiment is to predict the response of forest ecosystems to future concentrations of atmospheric carbon dioxide. The Duke Forest FACE site, located in a loblolly pine forest near Chapel Hill, NC, consists of three control FACE rings (ambient) and three treatment FACE rings that are fumigated with CO₂ enriched air (ambient+200 l l^-1 CO₂). Here we estimate annual gross primary productivity (GPP) of ambient and elevated CO₂ rings over the 6 years of CO₂ treatment using a process based model, PnET-Day. PnET-Day is a daily time step model which uses the relationship between foliar N concentration and maximum photosynthesis (A_max-N relationships) to calculate canopy photosynthesis. We parameterized the PnET-Day model with (A_max-N relationships measured through the canopy of both ambient and elevated CO₂ rings at the Duke Forest FACE site. The model was also parameterized with site-specific climate and vegetation variables to adjust canopy photosynthesis to estimate GPP. Mean annual GPP of the ambient grown forest was 2274 g C m^-2 yr^-1 while annual GPP of the elevated forest was 2586 g C m^-2 yr^-1. This represents a 14% stimulation of mean annual GPP by elevated CO₂ over the 6 years of CO₂ treatment and is in close agreement with the 18% stimulation of annual GPP by elevated CO₂ determined using biometric techniques at the Duke Forest FACE site.

Key words: gpp, elevated co₂, pnet model