ARS | Publication request: Photosynthetic photon flux density, carbon dioxide concentration and temperature influence photosynthesis in crotalaria species

Submitted to: The Open Plant Science Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 2012
Publication Date: March 19, 2012
Citation: Baligar, V.C., Bunce, J.A., Elson, M.K., Fageria, N.K. 2012. Photosynthetic photon flux density, carbon dioxide concentration and temperature influence photosynthesis in crotalaria species. The Open Plant Science Journal. 6:1-7.

Interpretive Summary: Perennial legume cover crops grown as an understory plant in cacao plantations could improve soil quality and suppress weeds. However, persistence of understory cover crops depends largely on the amount and quality of light reaching their canopies. Research was undertaken to evaluate the effects of light intensity, external temperature, and carbon dioxide concentrations on photosynthesis in four cover crop species. Increasing light intensity, temperature and carbon dioxide enhanced photosynthesis in all the species. These findings show that shade management of overstory trees is essential to the persistence and productivity of cover crops in cacao plantations. Findings of this study could assist cacao farmers to develop shade management systems to improve growth and persistence of cover crops to enhance soil fertility and there by improve cacao productivity in degraded tropical soils.

Technical Abstract: Crotalarias are tropical legumes grown as cover crops or as green manure to improve soil fertility. As an understory plant in plantation systems, these cover crops receive low levels of irradiance and are subjected to elevated levels of CO2 and temperatures. A greenhouse experiment was conducted to evaluate the independent short-term effects of photosynthetic photon flux density (PPFD), external carbon dioxide concentration (Ca) and temperature (T) on net photosynthesis (PN), internal CO2 (Ci), stomatal conductance (gs) and transpiration (E) in four Crotalaria species (C. breviflora, C. mucronata, C. ochroleuca, C. spectabilis). These crotalarias responded differently to changing PPFD, Ca and T. In all the Crotalaria species, increasing PPFD from 50 to 1500 µmol m-2 s-1 increased PN by 21 fold, increased gs by 2.3 fold (136%), decreased Ci by 3.9 times, and increased E by 2.1 times. Increasing the external Ca from 100 to 1000 cm3 m-3 increased PN by 4.7 fold, decreased gs by 1.3 times, increased Ci by 28 fold, and decreased E by 1.2 times. Increasing the T from 25 to 35 °C increased PN of Crotalaria species by 11%, decreased gs by 33%, decreased Ci by 64%, and increased E by 56%. Shade management is critical to maintaining the productivity of these tropical legumes.