Response of cocoa trees (Theobroma cacao) to a 13-month desiccation period in Sulawesi, Indonesia

Abstract

In South-east Asia, ENSO-related droughts represent irregularly occurring hazards for agroforestry systems containing cocoa which are predicted to increase in severity with expected climate warming. To characterize the drought response of mature cocoa trees, we conducted the Sulawesi Throughfall Displacement Experiment in a shaded (Gliricidia sepium) cocoa agroforestry system in Central Sulawesi, Indonesia. Three large sub-canopy roofs were installed to reduce throughfall by about 80% over a 13-month period to test the hypotheses that (i) cocoa trees are sensitive to drought due to their shallow fine root system, and (ii) bean yield is more sensitive to drought than leaf or stem growth. As 83% of fine root (diameter \2 mm) and 86% of coarse root biomass ([2 mm) was located in the upper 40 cm of the soil, the cocoa trees examined had a very shallow root system. Cocoa and Gliricidia differed in their vertical rooting patterns, thereby reducing competition for water. Despite being exposed for several months to soil water contents close to the conventional wilting point, cocoa trees showed no significant decreases in leaf biomass, stem and branch wood production or fine root biomass. Possible causes are active osmotic adjustment in roots, mitigation of drought stress by shading from Gliricidia or other factors. By contrast, production of cocoa beans 123Agroforest Syst (2010) 79:171-187 DOI 10.1007 was significantly reduced in the roof plots, supporting reports of substantial reductions in bean yields during ENSO-related drought events in the region. We conclude that cocoa possesses traits related to drought tolerance which enable it to maintain biomass production during extended dry periods, whereas bean yield appears to be particularly drought sensitive.

Spatial and temporal effects of drought on soil CO<sub>2</sub> efflux in a cacao agroforestry system in Sulawesi, Indonesia

“…Other studies by Harteveld et al (2008) and Kummerow et al (1982) confirm that cacao fine roots extend well beyond the stem and are primarily concentrated in the uppermost 30 cm. Although overall autotrophic respiration rates appeared to decline, Moser et al (2010) reported that cacao and Gliricidia fine root biomass remained unchanged at all soil depths to 250 cm, over the duration of the 13-month induced drought. These findings suggest that regardless of the drought stress the trees still continued to maintain and build new fine roots required to search for available water resources.…”

“…Additionally, a root excavation exercise done by Moser et al (2010) at the site, found that coarse roots of both cacao and Gliricidia were primarily concentrated around the tree stems while fine root (diameter<2 mm) distributions extended well into the agroforestry plantation. Other studies by Harteveld et al (2008) and Kummerow et al (1982) confirm that cacao fine roots extend well beyond the stem and are primarily concentrated in the uppermost 30 cm.…”

“…The presence or absence of deep root systems is one such response mechanism. Studies carried out in tropical forests of Latin America suggest that ecosystems with deep rooted trees are more capable of mitigating drought effects (Davidson et al, 2004;Nepstad et al, 1994).…”

Does Criollo cocoa have the same ecophysiological characteristics than Forastero?

“…Low photosynthetic rates (A) and stomatal conductance (g s ) have been reported in cocoa trees with reductions due to water deficit, high vapor pressure deficit (VPD) and high photosynthetic photon flux density (PFD) among other abiotic factors that could cause stress (Deng et al 1989;de Almeida and Valle 2007;Acheampong et al 2013;Ávila-Lovera et al 2016). There are limited studies on ecophysiological responses to water and light availability of different genotypes of adult cocoa trees, both in agricultural ecosystems and natural habitats (Moser et al 2010;Araque et al 2012;Jaimez et al 2013;Ávila-Lovera et al 2016).…”

Analysis of Agroecology and The Requirement of Supplemental Irrigation on Cacao Plants in Lampung

“…Tanaman kakao dikategorikan sebagai tanaman yang sensitif terhadap kekeringan (Carr & Lockwood, 2011). Kondisi defisit air akan lebih berpengaruh negatif terhadap hasil biji daripada pertumbuhan kakao (Moser et al, 2010). Radiasi matahari dan temperatur tinggi serta perbedaan kelembapan (tekanan uap) di udara dan di daun selama periode kekeringan/defisit air, berdampak negatif terhadap asimilasi CO 2 di dalam proses metabolisme kakao.…”