Nitrogen Interactions and Photosynthetic Responses to CO{sub 2}: Work Plan for Biocon Experiment/Physiological Measurements at Cedar Creek

Nitrogen plays a critical role in photosynthetic function, which in turn can affect many ecosystem processes through its effects on plant growth and ecosystem carbon cycles. As a result of its central role in photosynthetic enzymes, leaf N status can affect the magnitude of photosynthetic enhancement by elevated CO{sub 2}. It is now well-recognized that species responses to elevated CO{sub 2} may be different when species are grown in isolation vs. in a mixed community. Part of this effect may result from effects on leaf N itself as a result of species competition for N in N-limited ecosystems, and part of the effect is simply a function of dilution of leaf nutrients in leaves with greater carbohydrates as a result of elevated CO{sub 2}. However, photosynthetic efficiency itself may be affected if N-limited plants reallocate N within leaves away from carboxylation functions under elevated CO{sub 2} compared to ambient plants (Drake et al. 1997). Thus while there is cause to believe that there are interactive effects of N and CO{sub 2} on species photosynthetic physiology, there is little experimental data to support or reject this idea, particularity in realistic ecosystems under field conditions