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Title: Photosynthesis in tropical cover crop legumes influenced by irradiance, external carbon dioxide concentration and temperature

item Baligar, Virupax
item Bunce, James
item Elson, Marshall

Submitted to: Tropical Grasslands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2008
Publication Date: 1/3/2010
Citation: Baligar, V.C., Bunce, J.A., Elson, M.K., Fageria, N.K. 2010. Photosynthesis in tropical cover crop legumes influenced by irradiance, external carbon dioxide concentration and temperature. Tropical Grasslands. 44:24-32.

Interpretive Summary: Perennial legume cover crops grown as understory plants in cacao plantations offer a number of benefits, including protection from soil erosion, weed suppression, improved soil quality. However survivability and persistence of understory cover crops depends largely on the amount and quality of light reaching them. Research was undertaken to measure the effects of light intensity and external temperature, and carbon dioxide concentrations on the rate of photosynthesis in five tropical legume cover crop species. Increasing light intensity, temperature and carbon dioxide enhanced photosynthesis in these plants. Therefore shade management of overstory trees is very critical to maintain the persistence and productivity of these tropical perennial legumes. Findings of this research could help to develop shade management systems to improve the growth and persistence of cover crops in cacao plantations, and will be used by Researchers, Agriculture Extension personnel and cacao farmers.

Technical Abstract: In plantation crops perennial tropical legumes are grown as understory plants, receive limited irradiance, and are subjected to elevated levels of CO2 and temperature. Independent short-term effects of photosynthetic photon flux density (PPFD), external carbon dioxide concentration [CO2] and temperature on net photosynthesis (Pn) internal CO2 (Ci), stomatal conductance (Gs) and transpiration (E) were assessed in five tropical perennial legume cover crops (Calopo, Jack bean, Mucuna, White Lead Tree, Perennial Peanut). These legumes responded differently to changing PPFD, external [CO2] and temperature. In all legume species studied, increasing PPFD from 50 to 1000 µmol m 2 s 1 increased Pn by 11 fold. Increasing the external [CO2] from 250 to 700 µmol mol-1 increased Pn by two fold. Increasing temperature from 30 to 35°C reduced Pn in Calopo, Jack bean and Mucuna and increased Pn in White Lead Tree and Perennial Peanut. Gs increased with PPFD in all species except Perennial Peanut. Gs decreased substantially with [CO2] only in White Lead Tree, and changed little with temperature changes in any species. Perennial legumes studied here have shown that leaf photosynthesis would perform normally under rising atmospheric [CO2], temperature and PPFD in the absence of other abiotic stresses such as soil acidity, moisture and nutrients.