Partitioning of Net Ecosystem Exchange from Agroecosystems into Photosynthesis and Respiration.

Environmental and management factors are critical in determining the carbon source or sink status of agro-ecosystems. Information of carbon dynamics of an ecosystem from source to sink and vice-versa are critical in determining the role of that ecosystem in regional and global carbon balance.  Carbon dioxide flux between the vegetation and atmosphere was measured using an eddy covariance flux tower established in the middle of a cotton (Gossypium hirsutum L.) field. Using eddy covariance, the carbon dioxide flux is determined as the covariance between vertical wind velocity and carbon dioxide concentration. Eddy covariance has been widely used around the world for studying the carbon and hydrological cycles of different ecosystems. During daytime, the net ecosystem change (NEE) measured using eddy covariance represents the balance between carbon dioxide that is absorbed by the plant canopy through photosynthesis (gross primary production, GPP) and carbon dioxide that is released through a combination of autotrophic and heterotrophic respiration from the ecosystem (ecosystem respiration, Reco).  At night, the eddy covariance measurements of NEE represent Reco.  We also made soil respiration measurements using automated soil flux chambers.  Our results indicate that net ecosystem exchange, ecosystem respiration, soil respiration and gross primary production for this agro-ecosystem were strongly affected by environmental variables. Additional results from this study will be presented at this meeting.