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Abstract
The major products of photosynthesis in plants are nonstructural carbohydrates, sugars and starch. Sugars serve as transport molecule and intermediate in cell metabolism while starch acts a storage molecule, sequestering the energy and carbon for later use. Because they sit at the intersection of plant photosynthesis and the rest of plant metabolism, nonstructural carbohydrates interact with the major carbon fluxes in plant physiology such as photosynthesis and respiration. Furthermore, excess photosynthesis need not be all allocated to growth. Observations of nonstructural carbohydrate dynamics might indicate the status of plant carbon balance or the priority of storage relative to growth. Despite a number of experiments over more than 20 years, many aspects of nonstructural carbohydrate dynamics remain mysterious. We study these dynamics in an effort to render the mysterious obvious. We present three main results. The first is that simple feedbacks can create a number of dynamical phenomena (such as lag or hysteresis) in seasonal nonstructural carbohydrate dynamics. The second is an experiment on the post-drought change in seasonal nonstructural carbohydrate dynamics, for which we employ the first result. The third is that feedbacks provide important structure for ecosystem models, especially when implementing nonstructural carbohydrate models. Taken together, these results suggest that a simple feedback loop is sufficient to describe much of the heretofore mysterious nonstructural carbohydrates dynamics; however, much work to confirm and elaborate on these ideas remains.