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,Marshall K Elson,Alex-Alan F Almeida,Zhenli He,Quintino R De Araujo,Dario Ahnert

doi:10.3390/agronomy11020397

Virupax C Baligar, Marshall K Elson + Show 4 more

Open Access

https://doi.org/10.3390/agronomy11020397

Copy DOI

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 dioxide 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 and net assimilation rates increased, and specific leaf area decreased significantly in response to increasing carbon dioxide and PPFD. Increasing carbon dioxide and PPFD levels significantly increased net photosynthesis and water-use efficiency traits but significantly reduced stomatal conductance and transpiration. With few exceptions, increasing carbon dioxide and PPFD reduced macro–micro nutrient concentrations but increased uptake, influx, transport and nutrient use efficiency in all cacao genotypes. Irrespective of levels of carbon dioxide and PPFD, intraspecific differences were observed for growth, physiology and nutrient use efficiency of cacao genotypes.

Highlights

Cacao (Theobroma cacao L) is native to the understory of the Amazonian forests ofSouth America
Growth and development of young cacao trees are better under shade; heavy shade is detrimental to growth and production of matured and older trees [5,6,7,8]
When the cacao tree is grown in full sun, there can be no limitations of water and mineral nutrients in the soil

Summary

Introduction

Cacao (Theobroma cacao L) is native to the understory of the Amazonian forests ofSouth America. Cocoa is a C3 species and prefers full sun, but is tolerant to moderate shading, due to its phenotypic plasticity for acclimatization in moderate shade conditions [9]. It does not tolerate dense shade, where pod production is low, even with adequate water levels and mineral nutrients availability in the soil. When the cacao tree is grown in full sun, there can be no limitations of water and mineral nutrients in the soil. In a long-term field study in Ghana, Amelonado cacao trees in full sun yielded three times as much as shaded trees; the economic life of unshaded trees did not last more than 10 years of intensive cropping due to infestation of diseases and insects and loss of needed soil nutrients [10]. There is no universal agreement on the degree of shade required to maximize production of cacao grown under different tropical ecosystems of the world [9,11,12,13]

Objectives

Methods

Results

Conclusion