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发贡献大气水分。然而，在该地区，利用涡动相关技术直接测量二氧化碳和水蒸气通量的方法很少。我们之前在Bariri站点（印度尼西亚苏拉威西岛中部的热带山地雨林）的测量显示，该站点的碳吸收量和蒸散量出乎意料地大。因此，我们现在在扩展提案中提议调查一些系统问题，并测试一些可以解释观察结果的生物学假设。在工作包WP1中，我们希望(a)通过增加CO2和H2O剖面系统，改善夜间的测量，这通常是低估生态系统呼吸的一个来源，从而高估净碳吸收量；(b)测试高海拔地区（平均海拔1440米）的相对低温，高辐射和水可用性导致高净碳吸收量的假设。(c)验证漫射辐射具有增强碳吸收作用的假设。WP1将结合涡旋相关方差测量和Bariri站点的附加气象测量，并使用多层生物物理模型CANVEG进行生态系统建模。在WP 2中，我们想把重点放在森林和大气之间的局部水循环导致高水可用性（在旱季也是如此）的假设上。我们的目标是通过在巴里基地使用稳定的水同位素测量来实现这一目标。为此，我们将(a)对Bariri热带雨林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发的水同位素组成，(c)通过叶片、木质部、土壤水分和降水的独立测量验证我们的估计，以及(d)通过改进/开发支持水同位素的多层生物物理模型CANVEG，将我们的测量整合到生态系统尺度上。我们预计，我们的研究将大大提高我们对中苏拉威西热带山地雨林碳通量和水通量的认识。这一点尤其重要，因为该地区已被选为联合国REDD计划在印度尼西亚的唯一试点项目，迫切需要完整雨林的可靠碳吸收数据作为参考。

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.