Ashe juniper (Juniperus ashei Buchholz) and escarpment live oak (Quercus fusiformis Small) are two of the most common woody species of the Edwards Plateau, an arid-to-semi-arid region of nearly 100,000 km² in central Texas. They have very different hydraulic strategies, yet they experienced similar mortality rates during an extreme drought in 2011. We measured J. ashei and Q. fusiformis sap flow velocities during summer dry periods of 2016 and 2017 at six micro-sites. Although these were years with more-or-less average summer conditions, both included significant dry periods. To estimate the relative rate of decrease in sap velocity for each species during the dry periods, we fit a Bayesian exponential decay model to the sap velocity time series for each tree. We found that Q. fusiformis trees were better able to maintain transpiration than J. ashei during dry periods at five micro-sites and were comparable at the sixth micro-site. We conclude that it is likely that Q. fusiformis can better maintain transpiration during dry periods than J. ashei, on average, and that in the case of these two species, greater cavitation resistance may not translate to greater drought resistance.

中文翻译：

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在夏季干燥条件下，抗气蚀的杜松比易气蚀的橡树更早停止蒸腾

杜松 ( Juniperus ashei Buchholz) 和悬崖活橡树 ( Quercus fusiformis Small) 是爱德华兹高原最常见的^两种木本植物，爱德华兹高原是德克萨斯州中部近 100,000 平方公里的干旱至半干旱地区。他们有非常不同的水力策略，但他们在 2011 年的极端干旱期间经历了相似的死亡率。我们测量了J. ashei和Q. fusiformis6 个微型站点 2016 年和 2017 年夏季干旱期的液流速度。尽管这些年份或多或少具有平均夏季条件，但两者都包括显着的干旱期。为了估计干旱期间每个物种的汁液速度下降的相对速率，我们将贝叶斯指数衰减模型拟合到每棵树的汁液速度时间序列。我们发现，在 5 个微型站点的干旱期，梭形梭状芽孢杆菌比J. ashei能够更好地维持蒸腾作用，并且在第 6 个微型站点具有可比性。我们得出结论，Q. fusiformis可能比J. ashei在干旱期间更能维持蒸腾作用平均而言，在这两个物种的情况下，更大的抗气蚀性可能不会转化为更大的抗旱性。