agronomy Article The Impact of Carbon Dioxide Concentrations and Low to Adequate Photosynthetic Photon Flux Density on Growth, Physiology and Nutrient Use Efficiency of Juvenile Cacao Genotypes Virupax C. Baligar 1,* , Marshall K. Elson 1, Alex-Alan F. Almeida 2 , Quintino R. de Araujo 2 , Dario Ahnert 2 and Zhenli He 3 1 USDA-ARS-Beltsville Agricultural Research Center, Beltsville, MD 20705, USA;
[email protected] 2 Department of Biological Science, State University of Santa Cruz, Ilhéus, BA 45650-000, Brazil;
[email protected] (A.-A.F.A.);
[email protected] (Q.R.d.A.);
[email protected] (D.A.) 3 IRREC, Institute of Food and Agriculture Sciience, University of Florida, Fort Pierce, FL 34945, USA; zhe@ufl.edu * Correspondence:
[email protected]; Tel.: +1-301-504-6492 Abstract: Cacao (Theobroma cacao L.) was grown as an understory tree in agroforestry systems where it received inadequate to adequate levels of photosynthetic photon flux density (PPFD). As atmospheric carbon dioxide steadily increased, it was unclear what impact this would have on cacao growth and development at low PPFD. This research evaluated the effects of ambient and elevated levels carbon Citation: Baligar, V.C.; Elson, M.K.; dioxide under inadequate to adequate levels of PPFD on growth, physiological and nutrient use Almeida, A.-A.F.; de Araujo, Q.R.; efficiency traits of seven genetically contrasting juvenile cacao genotypes. Growth parameters (total Ahnert, D.; He, Z. The Impact of and root dry weight, root length, stem height, leaf area, relative growth rate and net assimilation Carbon Dioxide Concentrations and rates increased, and specific leaf area decreased significantly in response to increasing carbon dioxide Low to Adequate Photosynthetic Photon Flux Density on Growth, and PPFD.