Abstract Coastal shoreline forests are vulnerable to seawater exposure, the impacts of which will increase due to sea-level rise, but the long-term adaptation strategies and vulnerability of coastal forests are not well understood. We used whole-tree transpiration, leaf water potential, tree-ring width, and tree-ring δ13C (a proxy for intrinsic water use efficiency, iWUE) to examine the long-term adaptation strategies of red maple (Acer rubrum) trees at the coastal interface (i.e., shoreline) and nearby upland in Maryland, USA. Red maple trees that grew along the shoreline and were exposed to slightly saline water (up to two PSU) had higher transpiration rates than those growing in the nearby upland forest during a wet year, but these differences disappeared during a normal precipitation year. Shoreline trees grew more slowly than upland trees over the last four decades, but these growth differences have disappeared in the last six years. Shoreline and upland red maple trees had similar variation in iWUE, indicating that higher transpiration rates of the seawater-exposed trees did not translate into differences in water use efficiency. There were no differences in predawn and midday water potential between upland and shoreline trees, suggesting no additional water stress occurs in shoreline trees. These findings indicate that mature red maple in our coastal study site maintains gas exchange and growth at a consistent or homeostatic level under slight soil salinity.

中文翻译：

---

沿海森林中海岸线和高地红枫 (Acer rubrum) 树之间的树木生长、蒸腾作用和水分利用效率

摘要 沿海海岸线森林易受海水暴露影响，其影响将因海平面上升而增加，但沿海森林的长期适应策略和脆弱性尚不清楚。我们使用全树蒸腾作用、叶水势、年轮宽度和年轮 δ13C（内在水分利用效率的代表，iWUE）来检查红枫（Acer rubrum）树在美国马里兰州的海岸界面（即海岸线）和附近的高地。沿着海岸线生长并暴露于微咸水（最多两个 PSU）的红枫树在潮湿的年份比在附近高地森林中生长的红枫树具有更高的蒸腾率，但这些差异在正常降水年份消失了。在过去的四年里，海岸线树木的生长速度比陆地树木慢，但这些生长差异在过去六年中已经消失。海岸线和高地红枫树的 iWUE 变化相似，表明暴露于海水的树木较高的蒸腾速率并未转化为水分利用效率的差异。高地和海岸线树木之间的黎明前和中午水势没有差异，表明海岸线树木没有出现额外的水分压力。这些发现表明，我们沿海研究地点的成熟红枫在轻微的土壤盐分下保持气体交换和生长在一致或稳态水平。表明暴露于海水的树木较高的蒸腾速率并未转化为用水效率的差异。高地和海岸线树木之间的黎明前和中午水势没有差异，表明海岸线树木没有出现额外的水分压力。这些发现表明，我们沿海研究地点的成熟红枫在轻微的土壤盐度下保持气体交换和生长在一致或稳态水平。表明暴露于海水的树木较高的蒸腾速率并未转化为用水效率的差异。高地和海岸线树木之间的黎明前和中午水势没有差异，表明海岸线树木没有出现额外的水分压力。这些发现表明，我们沿海研究地点的成熟红枫在轻微的土壤盐分下保持气体交换和生长在一致或稳态水平。