Submitted to: Popular Publication
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/10/2004
Publication Date: 8/31/2004
Citation: Baligar, V.C., Bunce, J.A., Bailey, B.A., Machado, R.C., Pomella, A.W. 2004. Carbon dioxide and photosynthetic photon flux density effects on growth and mineral uptake parameters of cacao. Journal of Food Agriculture and the Environment 3:142-147. Interpretive Summary: The amount of sunlight falling on cocoa tree is known to affect its growth and yield. However, there is no universal agreement over the degree of shade or light quality that is required to maximize its production potentials. The concentration of carbon dioxide [CO2] in the atmosphere has risen in the last 110 years to 370 umol mol-1. It is expected to reach around 700 umol mol-1 sometime by the end of the 21st century. Higher [CO2]and loss of shade trees, coupled with low fertility of tropical soils, subjects cacao to severe stresses. Experiments were carried out in controlled environment glasshouses to assess the effects of [CO2] and light intensities and their interactions on physiological traits and nutrient use efficiency in cacao. Growth, mineral nutrient uptake, and nutrient use efficiency, in cacao were profoundly influenced by [CO2] and light intensities. High light intensity was detrimental to cacao growth and increasing [CO2] increased the growth and nutrient demand in cacao. In low fertility tropical soils, nutrient management is going to be very critical to maintain yield potentials of cacao, especially in increasing global [CO2] and loss of shade. Use of proper shade trees and input of adequate fertilizers appear to be important strategies in improving cacao yields in resource-poor tropical regions.
Technical Abstract: In recent years, carbon dioxide concentration [CO2] in the atmosphere has risen to 370 umol mol -l, with levels expected to double by the end of the 21st century. A climatically-controlled greenhouse experiment was undertaken to assess the influence of [CO2] and photosynthetic photon flux density (PPFD) on the growth, mineral nutrient uptake, and mineral nutrient use efficiency parameters of cacao (Theobroma cacao L) in its early growth stages. Plants were grown in two greenhouses and maintained at two levels of [CO2] (380 and 700 umol mol-l). In each greenhouse, three levels of PPFD, (65, 190, 1050 umol m-2 s-1) were achieved by constructing mini shade frames covered with various layers of plastic shade cloth. Plants were grown for 57 days. At all levels of PPFD, with few exceptions, increasing [CO2] tended to increase shoot and root growth parameters, (dry wt. of roots, stem and leaves, stem height, leaf area, shoot/root ratio, leaf area ratio, and relative growth rate). Both [CO2], and increasing PPFD from 65 to 190 umol m-2 s-1 increased growth parameters. At both [CO2] levels, PPFD of 1050 umol m-2 s-1 was detrimental to growth and to mineral nutrient uptake parameters. However, its effects were more severe at 380 than 700 umol mol-l of [CO2]. At all PPFD with few exceptions, increasing [CO2] increased the uptake of all mineral nutrients. With some exceptions, at both [CO2] levels increasing PPFD increased nutrient influx (IN) for Na, B, Mn, and Zn and decreased IN for other mineral nutrients. With some exceptions, at both [CO2] levels increasing PPFD decreased nutrient transport (TR) for Na and S and increased TR for Mg, B, and Zn only. At both [CO2] with the exception of nutrient use efficiency ratio (ER) for B, increasing PPFD increased ER for N, Na, S, and Zn, decreased ER for other mineral nutrients. At all PPFD levels, with few exceptions, overall, increasing [CO2] increased ER for N, Na, Mg, Cu, Mn, and Zn and decreased ER for other mineral nutrients. Growth, mineral nutrient uptake parameters and nutrient use efficiency ratios in cacao were influenced by [CO2] and PPFD. Overall, PPFD of 190 umol m-2 s-1 appears to be a desirable light intensity and combined with increasing [CO2] are beneficial in improving cacao growth and mineral nutrient uptake and use efficiency.