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Research Project: Characterizing and Evaluating the Genetic Diversity and Horticultural Value of Genetic Resources for Cacao and Other Tropical tree crops Economically important to the United States

Location: Sustainable Perennial Crops Laboratory

Title: The impact of ambient and elevated [CO2] and low to adequate photosynthetic photon flux density on growth, physiology and nutrient use efficiency of juvenile cacao genotypes

Author
item Baligar, Virupax
item Elson, Marshall
item ALMEIDA, A-A - University Of Santa Cruz - Brazil
item ARAUJO, Q - University Of Santa Cruz - Brazil
item AHNERT, D - University Of Santa Cruz - Brazil
item HE, Z - University Of Florida

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2021
Publication Date: 2/23/2021
Citation: Baligar, V.C., Elson, M.K., Almeida, A., Araujo, Q.R., Ahnert, D., He, Z. 2021. The impact of ambient and elevated [CO2] and low to adequate photosynthetic photon flux density on growth, physiology and nutrient use efficiency of juvenile cacao genotypes. Agronomy. https://doi.org/10.3390/agronomy11020397.
DOI: https://doi.org/10.3390/agronomy11020397

Interpretive Summary: In South America cacao is invariably grown as understory plants and are subjected to various degrees of shading. Growth and development of young cacao trees are better under shade, however, heavy shade is detrimental to growth and production of matured and older trees. Additionally, the effect of increasing concentrations of [CO2] in the atmosphere and its impact on the different levels of shading on cacao growth and development is unknown. In this paper we report our findings of the effects of increasing [CO2] and reduced shading on seven genetically contrasting juvenile cacao genotypes. We found significantly increased growth, net photosynthesis (PN) and water-use efficiency (WUE) and the existence of intraspecific differences for growth and nutrient use efficiencies. This information will be useful to cacao breeder selecting for superior cacao cultivars that have high nutrient and water use efficient under increasing levels of [CO2] and shade thus providing useful adaptable cacao genotypes for heavily shaded agroforesty systems.

Technical Abstract: Cacao (Theobroma cacao L.) is grown as an understory tree in agroforestry systems where it receives inadequate to adequate levels of photosynthetic photon flux density (PPFD). As atmospheric [CO2] are steadily increasing, it is unclear what impact this will have on cacao growth and development at low PPFD. This research evaluated the effects of ambient and elevated levels [CO2] under inadequate to adequate levels of PPFD on growth, physiological and nutrient use efficiency traits of seven genetically contrasting juvenile cacao genotypes. Growth parameters (total and root dry weight, root length, stem height, leaf area, relative growth rate (RGR), and net assimilation rates (NAR) increased and specific leaf area decreased significantly in response to increasing [CO2] and PPFD. Increasing [CO2] and PPFD levels significantly increased net photosynthesis (PN) and water-use efficiency (WUE) traits but significantly reduced stomatal conductance (gs) and transpiration (E). With few exceptions, increasing [CO2] and PPFD reduced macro-micro nutrient concentrations (C), but increased uptake (U), influx (IN), transport (TR) and nutrient use efficiency (NUE) in all cacao genotypes. Irrespective of levels of [CO2] and PPFD, intraspecific differences were observed for growth, physiology and nutrient use efficiency of cacao genotypes.