Effects of Developmental Changes on the Physiological Processes that Regulate Photosynthetic Responses to Climate Change

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Increasing atmospheric carbon dioxide concentrations and other atmospheric and climate changes may substantially alter plant growth. Differences in growth responses within and between plant species may have substantial impacts on biodiversity, carbon sequestration and other ecosystem functions by altering community composition and changing the movement of carbon, nutrients and water through ecosystems. However, despite extensive research over the last several decades, fundamental problems remain with predicting effects of climate change on plants. For example, carbon dioxide uptake by plants, a standard measure of climate change effects on carbon sequestration potential, has been found to vary substantially from carbon accumulation in plants. To account for this variability, a source-sink feedback mechanism is frequently invoked that links changes in carbon uptake (photosynthesis) with developmental changes that affect carbon accumulation. This mechanism is driven by changes in the balance between source activity (carbon uptake) and sink capacity (carbon accumulation). However, few studies have actually manipulated plant development to analyze the effects of normal developmental changes on physiological processes that regulate photosynthetic responses to climate change. As a result, the role of plant development in regulating photosynthetic responses to climate change is poorly understood. The overall goal of the proposed research is to develop a mechanistic understanding of the effects of developmental changes as plants age on the physiological processes that regulate photosynthetic responses to climate change. To identify key developmental and physiological processes that regulate photosynthesis, two key developmental processes, plant ontogeny (the timing and duration of developmental events) and morphological changes as plants age, will be independently manipulated. Planting cohorts of plants on different dates and inducing all cohorts to flower simultaneously will independently manipulate ontogeny and plant size. To avoid the confounding effect of accelerated ontogeny induced by growth in elevated carbon dioxide concentrations, a developmentally determinate, short-day species (Xanthium strumarium L.) will be used. In addition, because temperature is a key component of climate change and nitrogen supply is a critical factor regulating interactions between developmental and physiological processes, these factors will be manipulated to examine how they mediate the effects of developmental changes on photosynthesis. The results of this study will increase our understanding of the effects of changes in plant ontogeny and morphology on photosynthetic responses to climate change. More broadly, this study will increase our understanding of the links between carbon uptake and growth responses of plants to environmental change.