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，到世纪末，亚马逊雨林的大部分可能会消失，因为热带树木应该无法科普未来更高的温度和频繁的干旱。亚马逊雨林的这种“枯死”对全球变暖可能是灾难性的，因为亚马逊雨林中储存的大量碳将作为温室气体排放回大气中。这将加速全球变暖。这种情况是通过模拟植被对气候反应的计算机模型预测的。然而，目前还不清楚热带雨林树木对气候变化的敏感程度，如大气中二氧化碳浓度增加，温度升高和干旱。了解树木如何应对未来气候的一种方法是观察树木在过去对类似条件的反应。这样做的一个有效方法是使用树木年轮，因为它们提供了它们整个生命过程中生长速度的历史档案（即，200年或更长时间），这可能与环形成时的气候条件有关。因此，我建议使用树木年轮的热带树木，以评估如何敏感的树木一直在温度，干旱，太阳辐射的变化，并在大气中的CO2浓度增加在过去的世纪。我将测量树木年轮的宽度和稳定同位素浓度，以分析树木生长对气候和大气变化的反应。环宽测量将提供生长反应的洞察力，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，帮助了解任何生长反应背后的潜在过程。例如，通过研究生长率和植物用水的长期趋势，我将能够测试过去世纪二氧化碳浓度的增加是否确实刺激了热带树木的生长，正如人们经常提出的那样。通过将生长率的年与年之间的变化与干旱、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，并允许更好地评估亚马逊雨林在下一个世纪预计消失的可能性。

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.