Edwards 9807916 There is growing concern about predicted global climate change with parallel rises in carbon dioxide (C02) and temperature over the next 50 years, including questions of how this will impact agriculture and ecosystems. Plants have different mechanisms of assimilating C02 into organic matter, which will affect their responses to changes in climatic conditions. One type of plants, called C4 plants, have an active mechanism of accumulating C02 (a C02 concentrating mechanism). They make a substantial contribution to productivity on a global scale, and they also account for some of the world's worst weeds. There is currently speculation about how C4 plants would be affected by a global rise in C02 and temperature, and whether they would benefit, or would be threatened intrinscially by competition from other species. Fundamental to this question is a) understanding the mechanism of conversion of solar energy into adenosine triphosphate in C4 plants to power the C02 concentrating mechanism, and b) determining the magnitude of the diffusive resistance which allows the C02 to accumulate and limits its leakage from assimilating sites within the leaf. Wildtype plants of Amaranthus edulis (a C4 weed), and mutants which lack the C02 concentrating mechanism due to a defective C4 cycle, will be used to study these objectives. The other objective is to determine the response Of C4 plants to growth under current, two and three times current levels of C02 and to determine the interactive effects of temperature and light intensity. This will include measurements of photosynthetic rates, leaf expansion, content and activity of key proteins which catalyze conversion of carbon dioxide into carbohydrates in two C4 species, Amaranth and maize (corn), and one species, sunflower. A major question is whether C4 species can acclimate to C02 enrichment and rising temperatures and, thus, maintain a balance between key processes in carbon assimilation.
