Growth, Physiological and Nutrient Uptake Traits of Crotalaria Cover Crops Influenced by Levels of Carbon Dioxide under Low Light Intensities

Crotalarias are tropical legumes grown as cover crops or green manure crops to improve soil fertility and reduce soil degradation. As understory plants in plantation crop systems, these cover crops receive elevated levels of [CO2] and low irradiance. A greenhouse experiment was conducted to evaluate the effects of ambient (400 μmol mol-1) and elevated (700 μmol mol-1) levels of [CO2] at low photosynthetic photon flux density (PPFD) of 100, 250 or 450 µmol m-2 s-1 on growth, physiological and nutrient use parameters of four Crotalaria species (C. breviflora, C. mucronata, C. ochroleuca and C. spectabilis). Elevated [CO2] had little effect on growth, but increased NAR and nutrient use efficiency of N, Cu, Fe and Zn. PPFD had significant effects on growth, physiology and NUE. Increasing PPFD increased nutrient use efficiency of N and K, but reduced nutrient use efficiency of P and micronutrients. At low light intensities irrespective of [CO2], intraspecific differences were observed in crotalaria for growth, physiology and nutrient uptake traits. Irrespective of [CO2] levels at low PPFDs, C. mucronata was efficient in N, Ca, Cu, and Zn use efficiency and C. spectabilis was efficient in P, Ca, Mg, Fe, and Mn use efficiency.