Plant productivity is largely dependent on the photosynthesis rate of leaf canopies throughout the growing season. Because the environment surrounding a leaf is constantly changing, plants must modify the photosynthetic apparatus to compensate for the effect of environmental change if they are to maintain high rates of productivity. While recent work has focused on elucidating mechanisms of the photosynthetic response to rapid, short-term change in the environment, understanding of the mechanisms driving acclimation to seasonal, long-term change is limited. This work will study the mechanisms controlling the acclimation of photosynthesis to long-term changes in the environment, specifically light and CO2. The principal hypothesis is that following a change in light intensity or ambient CO2 level, the amount of protein invested in the component processes of the photosynthetic apparatus will be adjusted so that a balance is maintained between each step in the photosynthetic pathway. Thus, if a change in the environment leads to a single step limiting photosynthesis, nitrogen and carbon would be reallocated from nonlimiting processes and invested into the limiting process, increasing the rate of the limiting process and the overall photosynthesis rate. In fully acclimated plants, resources may be allocated optimally so that no single step limits photosynthesis. This work will improve understanding of the factors limiting growth, photosynthesis, and resource use efficiency in realistic environments. Our ability to identify beneficial traits, and to model and predict the performance of crop as well as wild plants will be substantially enhanced. In light of the significant change in global environments, particularly with respect to atmospheric warming and rising CO2, an improved ability to predict how plants respond to long-term environmental change will be invaluable for estimating the impact of global change on natural and agricultural ecosystems.
