Twentieth century changes of tree ring isotopes in Southeastern Brazilian forests: How do climate conditions influence growth and water use efficiency (WUE) and thus enforce tree migration

在IPCC之后，有强有力的证据表明，全球气温在不到150年的时间里上升了1°C，而大气中的二氧化碳浓度增加了30%以上。这种部分人为的影响提出了一个重要的问题，即这些人为活动在多大程度上干扰了热带和亚热带森林的生态生理需求。要了解不断变化的环境强迫对生态系统的影响，特别是对树木的影响，需要了解本地生长树木的年代际到百年变化的基本知识。因此，通过在较长时间内创建高度分辨率的区域和时间环境数据集来了解活树的长期行为是至关重要的。因此，通过测量各自的参数（树木年轮增量、稳定同位素等）来记录它们的时间行为，可以直接或通过树木的生理反应揭示树木在其环境中的大部分健康状况。我们研究的目的是在区域尺度上量化树木对水利用效率（WUE）和蒸腾的自然长期反应。重点集中在巴西<s:1>圣保罗州的亚热带样带。这将为阐明过去树木的发展和预测树木的动态，特别是在气候变化的世界中树木的生长铺平道路。为了实现这些目标，可以成功地计算出所有四个站点的增长率。总共计算和测量了4万多个树木年轮，用于同位素分析的1万个样本中有7000个已经打包。下一步将包括发展同位素年表、重新分析气候数据和计算WUE。从巴西水务局获得了<s:1>圣保罗州120多个站点的气候数据集（降水和河流测量）。此外，还提供了在Caetetus和Carlos Botelho站点测量的每日微气象数据（2003-2004年）。对于Vassununga站点，涡动相关通量塔数据可用于解释2棵树的年内同位素分析（相对湿度）。这个练习还会得出一个令人兴奋的结论，即主要使用的iWUE可以取代真正的WUE。iWUE的使用是一种权宜之计，因为相关的气象数据（rh）大多不存在。如上所述，几乎所有关于用水效率的研究都只考虑用水效率。这就不能把同化速率A和气孔导度gs在水分利用效率变化中的贡献分开。对同一棵树年轮中稳定碳和氧同位素的联合测量为解决这一问题提供了一个有希望的开端。这有助于了解树木对气候、气候变率（如ENSO）和二氧化碳驱动的树木生理变化的反应。

Following IPCC, there is strong evidence that the global temperature has risen by 1°C in less than 150 years while the atmospheric CO2 concentration increased by more than 30%. This partly man-made effect raises the important question to what extent these anthropogenic activities interfere with the ecophysiological requirements of tropical and subtropical forests. To understand the effects of changing environmental forcing on ecosystems and in particular on trees requires a basic knowledge about the decadal to centennial variability of indigenously growing trees. Consequently, it is of utmost importance to understand the long term behavior of living trees by creating highly resolved regional and temporal environmental data-sets over longer periods of time. Therefore, recording their temporal behavior by measuring the respective parameters (tree ring increment, stable isotopes etc.) reveals either directly or through tree physiological reactions much of the wellbeing of trees in their environment.The objective of our study is to quantify the natural long term reactions of trees with regard to water use efficiency (WUE) and transpiration on a regional scale. The emphasis is concentrated on a subtropical transect across the State of São Paulo, Brazil. This should pave the way for elucidating the tree development of the past and for predicting tree dynamics in particular tree growth in a climatically changing world. In order to achieve these goals growth rates from all four sites could successfully be calculated. Altogether, more than 40.000 tree rings were counted and measured and 7.000 out of 10.000 samples for isotope analysis are already packed. Next steps will include the development of isotope chronologies, reanalyzes of climate-data and the calculation of the WUE.Climate data sets (precipitation and river gauges) for more than 120 stations in the State of São Paulo were obtained from the Brazilian water agency. Additionally daily micrometeorological data (2003-2004) measured at the sites Caetetus and Carlos Botelho have been provided. For the site Vassununga even eddy covariance flux tower data are available for interpretation of the intra-annual isotope analyses of 2 trees (relative humidity). This exercise should additionally lead to the exciting conclusion of how trustworthy the predominantly used iWUE can replace the genuine WUE. The usage of the iWUE is a stopgap because the relevant meteorological data (rh) are mostly non-existent.As mentioned above almost all studies about WUE consider only the iWUE. This does not permit to separate the contribution of the assimilation rate A from that one of the stomatal conductance gs in the alteration of the WUE. The joint measurement of the stable carbon and oxygen isotopes in the same tree ring provides a promising start to solve this problem. This allows understanding the tree reactions to climate, climate variability (e.g. ENSO) and respectively CO2 driven changes in tree physiology.