Identifying environmental drivers of carbon and water fluxes and the origin of atmospheric water over a tropical mountain rainforest in Sulawesi, Indonesia

东南亚的热带雨林是区域气候系统的重要组成部分，因为它们吸收二氧化碳，并通过蒸散作用促进大气水分。然而，使用涡旋协方差技术直接测量二氧化碳和水蒸气通量在该地区很少。我们之前在印度尼西亚中苏拉威西的热带山地雨林巴里里进行的测量显示，出人意料的是大量的碳吸收和大量的蒸散。因此，我们现在建议在扩展提案中调查一些方法问题，并测试几个可以解释观察到的生物学假设。在工作包WP1中，我们想要(A)通过增加一个二氧化碳和H2O剖面系统来改进夜间测量，这通常是低估生态系统呼吸并从而高估净碳吸收的来源，(B)测试由于高海拔地点(1440 m a.s.l)相对较低的温度的假设。高辐射和水可获得性导致高净碳吸收，以及(C)检验漫射辐射具有促进碳吸收作用的假设。WP1将把Bariri站点的涡旋协方差测量和额外的气象测量与使用多层生物物理模型CANVEG的生态系统建模结合起来。在WP2中，我们想重点研究这样一个假设，即当地森林和大气之间的水循环导致了高的水可获得性(在旱季也是如此)。我们的目标是通过在巴里里遗址使用稳定的水同位素测量来实现这一点。为此，我们将(A)对巴里里热带雨林上空的大气水蒸气同位素测量进行连续测量，(B)使用通量梯度方法估计蒸散的水同位素组成，(C)通过对叶片、木质部、土壤水和降水的独立测量来验证我们的估计，以及(D)通过改进/开发多层生物物理模型CANVEG的水同位素版本，将我们的测量结果与生态系统规模相结合。这一点特别重要，因为该地区已被选为联合国REDD方案在印度尼西亚的唯一试点项目，迫切需要可靠的完整热带雨林的碳吸收数量作为参考。

Tropical rainforest in Southeast Asia are important components of the regional climate system as they absorb carbon dioxide and contribute to atmospheric moisture via evapotranspiration. Direct measurements of carbon dioxide and water vapour fluxes using the eddy covariance technique are, however, scarce in that region. Our previous measurements at the Bariri site, a tropical mountain rainforest in Central Sulawesi/Indonesia, revealed an unexpectedly large carbon uptake and large evapotranspiration. Thus, we now propose in the extension proposal to investigate a number of methodical questions and to test several biological hypotheses that could explain the observations.In work package WP1 we want to (a) improve the measurements at nighttime, which are often a source of underestimation of ecosystem respiration and thus overestimation of net carbon uptake, by adding a CO2 and H2O profile system, (b) to test the hypotheses that relatively low temperature due to the high elevation site (1440 m a.s.l.) with high radiation and water availability results in high net carbon uptake, and (c) to test the hypotheses that diffuse radiation has an carbon uptake enhancing effect. WP1 will combine eddy covariance measurements and additional meteorological measurements at the Bariri site with ecosystem system modeling using the multi-layer biophysical model CANVEG.In WP 2 we want to focus on the hypothesis that local water recycling between forest and atmosphere results in high water availability (also during the dry season). We aim to achieve this by using stable water isotope measurements at the Bariri site. For that we will (a) carry out continuous measurements of atmospheric water vapour isotope measurements over the tropical rainforest in Bariri, (b) estimate the water isotope composition of evapotranspiration using a flux-gradient approach, (c) validate our estimate with independent measurements of leaf, xylem, soil water and precipitation, and (d) integrate our measurements to ecosystem scale by improving/developing a water isotope enabled version of the multi-layer biophysical model CANVEG.We anticipate that our research will substantially improve our understanding of the carbon and water fluxes at the tropical mountain rainforest in Central Sulawesi. This is particularly of importance as this region has been selected as the only pilot project in Indonesia of the UN REDD program and reliable numbers of carbon uptake by the intact rainforest are urgently needed as reference.