Response of cocoa trees (<Emphasis Type="Italic">Theobroma cacao</Emphasis>) to a 13-month desiccation period in Sulawesi,Indonesia |
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| Authors: | G Moser C Leuschner D Hertel D Hölscher M Köhler D Leitner B Michalzik E Prihastanti S Tjitrosemito L Schwendenmann |
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| Institution: | 1.Plant Ecology, Albrecht von Haller Institute for Plant Sciences,University of G?ttingen,G?ttingen,Germany;2.Department of Tropical Silviculture and Forest Ecology, Burckhardt Institute,University of G?ttingen,G?ttingen,Germany;3.Department of Landscape Ecology, Institute of Geography,University of G?ttingen,G?ttingen,Germany;4.Department of Soil Sciences, Institute of Geography,University of Jena,Jena,Germany;5.Faculty of Mathematics and Natural Sciences,Diponegoro University,Semarang,Indonesia;6.Faculty of Biology,Bogor Agricultural University,Bogor,Indonesia;7.School of Environment,The University of Auckland,Auckland,New Zealand |
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| 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 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. |
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