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www.biogeosciences-discuss.net/6/11541/2009/
doi:10.5194/bgd-6-11541-2009
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Drought effects on soil CO2 efflux in a cacao agroforestry system in Sulawesi, Indonesia
1Buesgen-Institute, Soil Science of Tropical and Subtropical Ecosystems, Georg-August-University of Goettingen, Buesgenweg 2, 37075 Goettingen, Germany
2Burckhardt-Institute, Tropical Silviculture and Forest Ecology, Georg-August-University of Goettingen, Buesgenweg 2, 37075 Goettingen, Germany
3Department of Soil Science, Faculty of Agriculture, Bogor Agricultural University (IPB), Jl. Raya Pajajaran Bogor 16143, Indonesia
Abstract. Climate change induced droughts pose a serious threat to ecosystems across the tropics and sub-tropics, particularly to those areas not adapted to natural dry periods. In order to study the vulnerability of cacao (Theobroma cacao) – Gliricidia sepium agroforestry plantations to droughts a large scale throughfall displacement roof was built in Central Sulawesi, Indonesia. In this 19-month replicated experiment, we measured soil surface CO2 efflux (soil respiration) in three simulated drought plots compared with three adjacent control plots. Soil respiration rates peaked at intermediate soil moisture and decreased under increasingly dry conditions (drought induced), but also decreased when soils became water saturated, as evidenced in control plots. The simulated drought plots exhibited a slight decrease in soil respiration compared to the control plots (average 13% decrease). The strength of the drought effect was spatially variable – while some measurement chamber sites reacted strongly ("responsive") to the decrease in soil water content (up to R2=0.70) (n=11), others did not react at all ("non-responsive") (n=7). The degree of soil CO2 respiration drought response was highest around cacao tree stems and decreased with distance from the stem (R2=0.22). A significant correlation was measured between "responsive" soil respiration chamber sites and sap flux density ratios of cacao (R=0.61) and Gliricidia (R=0.65). Leaf litter CO2 respiration decreased as conditions became drier. During dry periods the litter layer contributed approximately 3–4% of the total CO2 efflux and up to 40% during wet periods. A CO2 flush was recorded during the rewetting phase that lasted for approximately two weeks, during which time accumulated labile carbon stocks mineralized. The net effect on soil CO2 emissions over the duration of the experiment was neutral, control plots respired 11.1±0.5 Mg C ha−1 yr−1, while roof plots respired 10.5±0.5 Mg C ha−1 yr−1.
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Notice on Discussion StatusCitation: van Straaten, O., Veldkamp, E., Köhler, M., and Anas, I.: Drought effects on soil CO2 efflux in a cacao agroforestry system in Sulawesi, Indonesia, Biogeosciences Discuss., 6, 11541-11576, doi:10.5194/bgd-6-11541-2009, 2009. Bibtex EndNote Reference Manager XML
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