|Allen, Leon - Hartwell|
Submitted to: Functional Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2009
Publication Date: 9/1/2009
Citation: Prasad, V., Vu, J.C., Boote, K.J., Allen Jr, L.H. 2009. Enhancement in leaf photosynthesis and up-regulation of Rubisco in the C4 sorghum plant at elevated growth carbon dioxide and temperature occur at early stages of leaf ontogeny. Functional Plant Biology. 36: 761-769. Interpretive Summary: Atmospheric carbon dioxide (CO2) level is expected to double within this century. Consequently, increases in air temperature (T) by as much as 4-6C have been predicted. Research on rising CO2 and temperature has focused mainly on C3 crops such as soybean and rice. Few tests, however, have done on C4 crops such as sorghum and maize. In this study, by scientists at the USDA-ARS and University of Florida in Gainesville, FL, grain sorghum was grown at ambient or twice-ambient CO2, and at daytime T of 30 and 36C, to characterize the effects of both high CO2 and T on leaf photosynthesis (Ps) and biomass production of this C4 crop at different growth stages of the leaf/plant. Ps is a process by which leaves absorb CO2 from the air to make compounds necessary for plant growth and yield. The results showed that, at 30C growth, biomass parameters (leaf, stem, and total plant) were not affected by high CO2 until 50 days after sowing. In contrast, at 36C, all biomass parameters were progressively enhanced by high CO2. In addition, the enhancement in leaf Ps by high CO2 occurred to a greater extent at high T during the early stages of leaf growth. Such enhancement would explain the increases in biomass of the C4 grain sorghum grown at high CO2 and temperature.
Technical Abstract: Grain sorghum was grown at 350 and 700 (high) ppm CO2, and at daytime maximum/nighttime minimum temperatures of 30/20 and 36/26C. Gas exchange rates, activities of Rubisco and PEP carboxylase (PEPC), leaf area, and biomass of various plant components were determined at different stages of leaf and plant growth. At 6-25 days after leaf emergence (DALE), CO2 exchange rate (CER) of high CO2 plants was 20-23% greater at 30/20C and 10-24% greater at 36/26C. The positive response of CER to high CO2 was greater in young leaves than old leaves. In young leaves, high CO2 enhanced Rubisco activity by 23% at 30/20C, and 17-74% at 36/26C. PEPC activity was not affected by high CO2 at 30/20C, but was enhanced by 13% at 36/26C at 6 DALE. At 30/20C, growth parameters (leaf, stem and total plant dry weights) were not affected by high CO2 until 50 days after sowing (DAS) when they were increased by 32-49%. In contrast, at 36/26C all growth parameters were progressively enhanced by high CO2, and were increased by 49-62% at 50 DAS. Thus, for the C4 sorghum, there was an enhancement in CER and Rubisco activity by high CO2 and temperature at early stages of leaf ontogeny, and such stimulation would contribute to increased plant biomass.