Can tropical Montane forest Acclimate to high temperature? Montane-Acclim

热带森林在全球水、碳和养分循环中发挥着关键作用，目前吸收了数十亿吨碳，从而减缓了气候变化的速度。因此，用于预测未来气候变化以及气候对植物和生态系统的影响的计算机模型需要能够很好地代表热带森林。事实上，热带森林对温度变化的反应是气候变化预测中最大的不确定性之一。然而，目前，科学家们还不清楚这些森林将如何应对气温上升。这是令人担忧的，因为今天的气温比过去上升得更快，迫使森林对前所未有的变暖速度做出反应。关键是，气温缺乏季节性变化可能意味着，与更温带和高纬度的树种相比，生长在这些地区的树木应对快速气候变化的能力降低。如果是这样的话，那么全球变暖可能会对这些森林、它们所包含的惊人数量的生物多样性以及它们在降低当前气候变化速度方面的作用构成相当大的威胁。然而，这一建议还有待正式检验。对于生长在山区的热带森林来说，缺乏理解更令人担忧，因为这些地区的气温上升速度比低地更快。例如，研究哥伦比亚和秘鲁安第斯森林的科学家观察到，一些原产于高海拔地区的树种正在灭绝，而另一些树种正在向更高海拔地区转移。这些科学家提出，这些观察结果可能是因为树木已经看到了气候变化的影响，无法承受当前的温度。然而，这一解释仍然存在争议，还没有得到正式检验。该项目的主要目标是确定热带安第斯物种是否能够忍受当前的温度，并做出调整，以承受未来预期的更高温度。为了回答这个问题，我们将在哥伦比亚安第斯山脉的高海拔地区种植树木，在它们的家园环境中，但也在温度分别高出5摄氏度和9摄氏度的两个较低海拔地区种植树木。我们的树木将全部种植在普通土壤中，并将获得充足的水，消除水和养分获取方面的潜在差异。我们将监测其他三个地点的光合作用、呼吸作用和生长情况，以了解它们对温度的反应。与其他实验相比，我们的研究是独一无二的，因为它将：i)第一次调查种植在普通土壤中的3-4m高大树木对长期(3年)温度变化的反应能力，ii)调查比所有其他关于这一主题的现场研究更多的物种数量，以及iii)测量比任何其他实验更完整的一套关键的生理和生长反应。所进行的测量将被用来推导出数学方程，该方程可以表示这些树木山地物种对高温的反应。此外，为了预测世界各地热带森林对高温的反应，我们需要尽可能多的地点的高海拔和低海拔数据。世界各地的科学家现在开始在哥斯达黎加、波多黎各、巴拿马、巴西、秘鲁、卢旺达和澳大利亚的森林中收集其中的一些测量数据。尽管这些调查中没有一个像我们的研究那样详细，但通过与所有这些小组合作，我们可以使用他们的数据来测试和推断我们在全球所有热带地区的方程式。然后，我们将把这些数学方程引入计算机模型，以预测热带森林在变暖条件下的未来行为。这一结果将代表着我们准确预测这一至关重要的生物群将如何应对全球变暖的能力发生了重大变化。

Tropical forests play a critical role in global water, carbon and nutrient cycles, and currently absorb billions of tonnes of carbon, thus reducing rates of climate change. For this reason, computer models that are used to predict future climate change and the impacts of climate on plants and ecosystems, need to be able to represent tropical forest very well. In fact, the response of tropical forests to changes in temperature is one of the greatest uncertainties in climate change prediction. However, currently, scientists do not understand how these forests will respond to increasing temperatures. This is worrying because temperatures are increasing faster today than in the past, forcing forests to respond to unprecedented rates of warming. Critically, the lack of seasonal changes in temperature may mean that trees growing in these regions have a reduced capacity to deal with rapid climate change compared with more temperate and high-latitude species. If this is the case, then global warming may represent a considerable threat to these forests, the amazing amounts of biodiversity that they contain, and their role in reducing current rates of climate change. However, this suggestion is yet to be tested formally.The lack of understanding is even more worrying for tropical forest growing in mountains, as in these areas temperatures are increasing faster than in the lowlands. For example, scientists studying Andean forest in Colombia and Peru have observed that some tree species native to high elevations are dying out while others are moving to higher elevations. These scientists have suggested that these observations may be explained by the fact that trees are already seeing the impacts of climate change and are not able to withstand current temperatures. However, this explanation remains controversial and has not been tested formally. The major goal of this project is to determine if tropical Andean species can tolerate current temperatures and adjust to withstand the higher temperatures expected for the future. To answer this question, we will plant trees from high elevations in the Colombian Andes in their home environment but also at two lower elevations where temperatures are 5oC and 9oC higher, respectively. Our trees will be all planted in common soils and will have access to plenty of water, eliminating potential differences in water and nutrient access. We will monitor photosynthesis, respiration and growth at the three locations in other to understand how they respond to temperature. Compared to other experiments, our study is unique as it will: i) be the first to investigate the ability of large 3 - 4m tall trees planted in a common soil to respond to long-term (3 year) changes in temperature, ii) investigate a much greater number of species than all other field studies on this subject, and iii) measure a more complete set of key physiological and growth responses than in any other experiment. The measurements taken will be used to the derive mathematical equations that can represent the response of these tree montane species to elevated temperatures. Furthermore, to predict the response of tropical forest everywhere in the world to higher temperatures, we need data from high and low elevations in as many locations as possible. Scientists around the world are now starting to collect some of these measurements in forests from Costa Rica, Puerto Rico, Panama, Brazil, Peru, Rwanda and Australia. Although, no one of these investigations is as detailed as our study, by teaming up with all these groups we can use their data to test and extrapolate our equations across all tropics globally. We will then introduce these mathematical equations into a computer model to predict future behavior of the tropical forest under warming conditions. The outcome will represent a step change in our ability to accurately predict how this critically important biome will respond to global warming.