Impact of Ambient and Elevated [CO2] in a Low Levels of Photosynthetic Photon Flux Density (PPFD) on Growth and Macro Nutrient Use Efficiency in Tropical Perennial Legume Cover Crops.

Climatic changes such as increasing global [CO₂] and low levels of PPFD at canopy levels may have great impact on growth, nutrient use efficiency and survivability of understory plants. In early years of establishment of plantation crops, soil erosion is a major cause of soil degradation. Under such situations, legume cover crops grown as understory plants could reduce nutrient loss through erosion and leaching, further help to higher C sequestration there by improve soil fertility. Research was undertaken to evaluate ambient (400 µmol mol^-1) and elevated (700 µmol mol^-1) carbon dioxide concentrations [CO₂] at low levels of PPFD  (100, 200, 400 ± 50 μmol m^-2 s^-1) on growth and nutrient use efficiency of perennial tropical legume cover crops. Among climbing and non climbing cover crop species, differential responses to ambient and elevated [CO₂] and low light intensities (PPFD) were observed for growth parameters. and nutrient use efficiency. Overall [CO₂], PPFD and cover crop species had significant effects on growth and macro-nutrient use efficiency in all the cover crops. Irrespective of levels of [CO₂] and PPFD in climbing cover crops, overall mucuna had the highest growth parameters, where as in non-climbing cover crops, with exception of SLA, overall perennial peanut had the highest growth parameter. Irrespective of levels of [CO₂] and PPFD in climbing cover crops, overall, calopo was most efficient in  P, Ca, and Mg use efficiency and mucuna was most efficient in N and K use efficiency, where as in non-climbing  cover crops ea-ea was most efficient in P, K, Ca and Mg use efficiency; however perennial peanut was efficient for N use efficiency only.