Role of Winter Water Relations in Determining the Upper Elevational Limits of Three New England Conifers

9603860种博伊斯常绿针叶树不同于危险的树木，它们必须在冬天保持树叶存活。除了冰冻胁迫，它们还必须应对干旱或干燥。在冬季环境中发现了大量的水，但它通常被锁住作为雪和冰，植物无法获得。针叶树叶适合在冬季最大限度地减少水分损失；在冰冻以上的时期，木材中储存的水分融化并可以流入树叶，从而弥补损失。在高海拔地区，较短的生长季节降低了叶片对冬季水分损失的抵抗力，同时冬季暖期的频率和持续时间也减少。因此，失水量增加，而补水能力下降。在一些地方，冬季的干燥似乎会导致高山林线。然而，它在设定不会一直延伸到树线的针叶树海拔上限方面的作用鲜为人知。这项研究将研究三种重要的新英格兰针叶树冬季水分关系或水分平衡，这些针叶树在位置偏好和生长策略上存在差异：白松、东部铁杉和红松。我们的初步数据表明，这些物种中较老的叶子在冬季可能会经历破坏性的水位。我们将使用在海拔上限附近收集的树木的生理测量来确定干燥压力。这些数据将与在研究地点收集的气候数据结合起来，以预测水关系。这种方法可以推广到其他物种，并在气候变化强加的条件下进行。

9603860 Boyce Evergreen conifers, unlike diciduous trees, must keep their foliage alive during the winter. In addition to freezing stress, they must deal with drought, or desiccation. A lot of water is found in the winter environment, but it is usually locked up as snow and ice and is unavailable to plants. Conifer foliage is adapted to minimize water loss during the winter; losses are replaced during above-freezing periods, when water stored in the wood melts and can flow into the foliage. Shorter growing seasons at high elevations decrease foliar resistance to winter water loss, while the frequency and duration of warm periods in the winter also decreases. Thus, the amount of water lost increases, while the ability to replace it decreases. Winter desiccation appears to cause alpine treeline in some places. However, its role in setting the upper elevational limits of conifers that do not extend all the way to treeline is poorly known. This study will examine the foliar winter water relations, or water balance, of three important New England conifers that differ in location preferences and growth strategies: white pine, eastern hemlock and red pine. Our preliminary data suggest that the older foliage in these species may experience damaging water levels during the winter. We will use physiological measurements of trees collected near their upper elevational limit to determine desiccation stress. These data will be coupled with climatic data collected at the research sites to predict water relations. This approach may be extended to other species and under conditions imposed by a changing climate.