Climate models project increased growing season air temperatures and decreased depth and duration of winter snowpack for the north‐eastern United States, leading to greater frequency of soil freeze/thaw cycles in winter over the next century. We utilized the Climate Change Across Seasons Experiment (CCASE) at Hubbard Brook Experimental Forest in New Hampshire to determine how projected changes in climate in this region affect the depth from which trees take up water, which to our knowledge has yet to be determined. We determined the stable isotopic composition of water in soils and branch xylem three times throughout the growing season to partition potential sources of water for red maple (Acer rubrum) trees. Using a Bayesian mixing model approach, we determined that all trees used similar water sources in the early (June) and mid (July) growing season. However, in the late growing season (August), trees exposed to ambient and warmer growing season soil temperatures took up more than 40% of their water from between 90‐ and 100‐cm soil depth, likely due to greater water availability at this depth. In contrast, those trees exposed to soil freeze/thaw cycles in winter utilized water from all depths (0–100 cm) evenly (8–10%), possibly due to soil freezing causing compensatory root growth in the following growing season, compared with trees in the reference and warmed plots. These results demonstrate that the projected changes in climate for the north‐eastern United States are likely to alter the depth from which trees access water, especially in the late growing season.

中文翻译：

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气候变化下北部硬木森林中红枫树的水源

气候模型预测，美国东北部生长季节的气温会升高，冬季积雪的深度和持续时间会减少，从而导致下一世纪冬季土壤冻结/融化循环的频率增加。我们利用新罕布什尔州哈伯德布鲁克实验森林的跨季节气候变化实验（CCASE）来确定该地区预计的气候变化如何影响树木吸水的深度，据我们所知，这尚待确定。我们确定土壤中的水稳定同位素组成与木质部分会在整个生长季节，为红枫的水分配潜在来源三次（宏碁癣菌）的树木。使用贝叶斯混合模型方法，我们确定所有树木在生长早期（6月）和中期（7月）都使用相似的水源。然而，在生长后期（八月），暴露于环境和较热生长季节土壤温度的树木从90到100厘米土壤深度吸收了超过40％的水分，这可能是由于该深度的可用水量更大。相比之下，与冬季相比，冬季暴露于土壤冰冻/融化周期的那些树木均匀地利用了所有深度（0–100厘米）的水（8–10％），这可能是由于土壤冰冻导致下一个生长季节补偿性根生长的原因。参考区和暖区中的树木。这些结果表明，美国东北部预计发生的气候变化可能会改变树木获取水的深度，