Impact of ambient and elevated [co2] in low light levels on growth, physiology and nutrient uptake of tropical perennial legume cover crops

Authors: Baligar, Virupax; Elson, Marshall; HE, Z - University Of Florida; LI, Y - University Of Florida; PAIVA, A - University Of Santa Cruz - Brazil; ALMEIDA, A - University Of Santa Cruz - Brazil; AHNERT, D - University Of Santa Cruz - Brazil

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2021
Publication Date: 1/20/2021
Citation: Baligar, V.C., Elson, M.K., He, Z., Li, Y., Paiva, A.D., Almeida, A.A., Ahnert, D. 2021. Impact of ambient and elevated [co2] in low light levels on growth, physiology and nutrient uptake of tropical perennial legume cover crops. Plants. https://doi.org/10.3390/plants10020193.
DOI: https://doi.org/10.3390/plants10020193

Interpretive Summary: Cacao trees are often established with wide row spacing on recently cleared, sloping land and such system of planting leads to soil degradation due to soil erosion and leaching loss of nutrients. Establishment of perennial legume cover crops before and during the early stages of cacao establishment could reduce soil degradation and suppress weeds. However, growth and persistence of perennial legume cover crops in cacao are affected by the level of light at their canopy levels and prevailing CO2 levels. In this paper we report the existence of intraspecific differences in perennial cover crops for growth, physiology, water use efficiency and macro and micronutrient use efficiency when grown at low levels of irradiance and at ambient and elevated CO2. This information will be useful to farmers to select most beneficial legume cover crops to grow under cacao trees and plant breeders to use these efficient legume cover crops in developing superior cover crops to reduce further soil degradation in plantation crops.

Technical Abstract: At early stages of establishment of tropical plantation crops inclusion of legume cover crops could reduce soil degradation due to erosion and nutrient leaching. As understory plants these cover crops receive limited irradiance and can be subjected elevated CO2 at ground level. A glasshouse experiment was undertaken to assess the effects of ambient (450 µmol mol-1) and elevated (700 µmol mol-1) levels of [CO2] on growth, physiological changes and nutrient uptake of six perennial legume cover crops (Perennial Peanut, Ea-Ea, Mucuna, Pigeon pea, Lab lab, Cowpea) under low levels of photosynthetic photon flux density (PPFD; 100, 200, and 400 µmol m-2 s-1). Overall, total and root dry biomass, total root length, specific leaf area, and relative growth rates were significantly influenced by levels of [CO2] and PPFD and cover crop species. With few exceptions, all the cover crops showed significant effects of [CO2], PPFD, and species on net photosynthesis (PN) and its components (gs, Ci, E). Increasing [CO2], from 450 to 700 µmol mol-1 and increasing PPFD from 100 to 400 µmol'm-2 's-1 increased PN. Overall, the levels of [CO2] and PPFD and species significantly affected total water use efficiency (WUETOTAL), instantaneous water use efficiency (WUEINST) and intrinsic water use efficiency (WUEINTS). With some exceptions, increasing levels of [CO2] and PPFD increased all the WUE parameters. Interspecific differences were observed with respect to macro-micro nutrient uptake and use efficiency. With a few exceptions, increasing levels of [CO2] from 450 to 700 µmol mol-1 and PPFD from 100 to 400 µmol m-2 s-1 increased nutrient use efficiency (NUE) of all nutrients by cover crop species.