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Drought effects on water relations in beech: the contribution of exchangeable water reservoirs.

机译：干旱对山毛榉中水关系的影响：可交换水库的贡献。

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The exceptional soil drought and heat wave that occurred in Europe in summer 2003 provided a good opportunity to analyze the response of forest ecosystems to extreme climatic conditions. This work aimed at studying the functioning of exchangeable water reservoirs of beech trees under climatic and edaphic constraints, in a 37-year-old beech stand located in north-eastern France. We characterised the impact of drought on seasonal variations in water fluxes at the tree (sap flow measurements) and the forest (eddy covariance measurements) scales and estimated (i) the daily water storage capacity of beech trees as the difference between stand-scaled sap flow and water vapour flux over the stand and (ii) the contribution of exchangeable water in tree reservoirs to the total tree transpiration, under non-limiting soil water (summer 2002) or severe soil drought conditions (summer 2003). In parallel, daily variations in trunk circumference were analyzed to estimate the contribution of elastic tissues as a compartment for water storage to tree transpiration. Stand transpiration was strongly reduced by soil water shortage (up to 80% at the peak of drought in August 2003). From the beginning of August 2003, we observed daytime contraction of stem circumference, with only partial, or even no night recovery, suggesting that trees were less and less able to refill the elastic and strongly depleted reservoirs. Even if those elastic reservoirs were active throughout the season, the corresponding volume of water withdrawn for tree transpiration remained very low (maximum 1% of the daily transpiration). Thus, elastic tissue reservoirs play a minor role in the total water budget of beech trees. The amount of water depleted daily from the whole reservoirs was much higher than the water extracted from elastic tissues. Furthermore, the contribution of total exchangeable water within trees to the transpiration stream increased during the dry period (from a few percent to 67% at the peak of the drought) and was positively correlated with soil water shortage. Our results thus clearly demonstrated the strong sensitivity of beech to both climate and drought and the major role of whole tree water reservoirs to maintain leaf transpiration under severe drought.Digital Object Identifier http://dx.doi.org/10.1016/j.agrformet.2010.12.008
机译：2003年夏季在欧洲发生的异常土壤干旱和热浪，为分析森林生态系统对极端气候条件的响应提供了一个很好的机会。这项工作旨在研究位于法国东北部拥有37年历史的山毛榉林分，在气候和水生条件下，山毛榉树可交换水库的功能。我们表征了干旱对树木（树汁流量测量）和森林（涡流协方差测量）尺度上水通量季节性变化的影响，并估计（i）山毛榉树的日蓄水量，作为标准规模树液之间的差异。在非限制性土壤水（2002年夏季）或严重土壤干旱条件下（2003年夏季），林分中的流量和水蒸气通量;（ii）树木水库中交换水对树木总蒸腾量的贡献。平行地，分析树干周长的每日变化以估计弹性组织作为储水室对树木蒸腾作用的贡献。土壤缺水极大地减少了林分蒸腾作用（2003年8月干旱高峰时高达80％）。从2003年8月开始，我们观察到茎干日间收缩，只有部分恢复，甚至没有晚上恢复，这表明树木越来越难以补充有弹性且严重枯竭的水库。即使这些弹性水库在整个季节都很活跃，用于树木蒸腾的相应抽水量仍然非常低（每天最多蒸腾1％）。因此，弹性组织储层在山毛榉树的总水量中只占很小的比例。每天从整个水库中消耗的水量要比从弹性组织中提取的水量高得多。此外，在干旱时期，树木内总交换水对蒸腾流的贡献增加（从干旱高峰时期的百分之几增加到67％），并且与土壤缺水成正相关。因此，我们的结果清楚地表明了山毛榉对气候和干旱都具有很强的敏感性，并且整个树木的水库在严重干旱下对维持叶片的蒸腾作用也起着主要作用。数字对象标识符http://dx.doi.org/10.1016/j.agrformet .2010.12.008

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