Climate change and the Amazon: assessing the impact of climate on tree growth using tree ring widths and isotopes

亚马逊雨林可能非常容易受到气候变化的影响。如果地球像预测的那样变暖，亚马逊雨林的大部分可能在本世纪末消失，因为热带树木应该无法应对未来更高的气温和频繁的干旱。亚马逊雨林的这种“死亡”可能会对全球变暖造成灾难性的影响，因为亚马逊雨林中储存的大量碳将以温室气体的形式排放回大气中。这将加速全球变暖。这种情景是通过模拟植被对气候的反应的计算机模型来预测的。然而，热带雨林树木对气候变化的敏感度仍然非常不确定，例如大气中二氧化碳浓度的增加、更高的温度和干旱。要深入了解树木将如何应对未来的气候，一种方法是观察树木过去对类似条件的反应。这样做的一个有效方法是使用年轮，因为它们提供了整个生命(即200年或更长时间)增长率的历史档案，这可能与年轮形成时的气候条件有关。因此，我建议使用热带树木的年轮来评估树木对上个世纪以来温度、干旱、太阳辐射和大气二氧化碳浓度增加的敏感程度。我将测量年轮宽度和年轮中的稳定同位素浓度，以分析树木生长对气候和大气变化的反应。年轮宽度测量将提供对生长反应的洞察，碳同位素将通过提供有关光合作用和植物水分利用的详细信息，帮助理解任何生长反应背后的潜在过程。例如，通过研究生长速度和植物用水量的长期趋势，我将能够测试过去一个世纪二氧化碳浓度的增加是否真的像人们经常提出的那样刺激了热带树木的生长。通过将生长速度的年际变化与干旱、温度和太阳辐射的变化联系起来，我将确定控制热带树木生长的主要气候因素。我的研究将提高我们对热带树木对预测的气候变化和大气二氧化碳增加的敏感性的理解，并使我们能够更好地评估下个世纪亚马逊雨林预计消失的可能性。

The Amazon rainforest may be very vulnerable to climate change. If the earth warms as predicted, much of the Amazon rainforest could disappear by the end of the century, as tropical trees should be unable to cope with higher temperatures and frequent droughts in the future. Such a 'die-back' of the Amazon rainforest could be disastrous for global warming, as the vast stores of carbon contained in the Amazon would be emitted back into the atmosphere as greenhouse gases. This will speed-up global warming. Such a scenario is predicted by computer models that simulate responses of vegetation to climate. However, it is still very uncertain how sensitive rainforest trees are to changes in climate like increasing atmospheric CO2 concentrations, higher temperatures, and droughts. One way of getting insights into how trees will respond to future climate is by looking at how trees have responded to similar conditions in the past. An effective approach of doing this is by using tree rings, as they provide an historical archive of growth rates over their entire life (i.e., 200 years or more), which can be related to the climate conditions at the time of ring-formation. Therefore, I propose to use tree rings of tropical trees to assess how sensitive trees have been to changes in temperature, drought, solar radiation, and increases in atmospheric CO2-concentrations over the last century. I will measure ring widths and stable isotope concentrations in tree rings to analyse the responses of tree growth to climatic and atmospheric changes. Ring width measurements will give insight in growth responses, and carbon isotopes will help understand the underlying processes behind any growth responses by giving detailed information on photosynthesis and plant water use. For example, by studying long-term trends in growth rates and plant water use, I will be able to test whether increases in CO2 concentrations over the past century have indeed stimulated tropical tree growth, as has often been proposed. By linking year to year variation in growth rates to variation in droughts, temperature and solar radiation, I will determine the main climatic factors controlling tropical tree growth. My study will improve our understanding of sensitivity of tropical trees to predicted changes in climate and increasing atmospheric CO2 and allow a better assessment of the likelihood of the predicted disappearance of the Amazon rainforest over the next century.