Abstract Salinity intrusion is responsible for changes to freshwater wetland watersheds globally, but little is known about how wetland water budgets might be influenced by small increments in salinity. We studied a forested wetland in South Carolina, USA, and installed sap flow probes on 72 trees/shrubs along a salinity gradient. Species investigated included the trees baldcypress (Taxodium distichum [L.] Rich.), water tupelo (Nyssa aquatica L.), swamp tupelo (Nyssa biflora Walt.), and the shrub waxmyrtle (Morella cerifera (L.) Small). This study improves upon past reliance on greenhouse seedling studies by adding measurements of trees/shrubs along a salinity gradient, and better describes the role of low salinity on water use in freshwater wetland forests. We measured patterns of water use related to salinity, atmospheric conditions and season, and hypothesized that salinity would influence wetland forest water use through two mechanisms: salinity disturbances would yield stands with species and size classes that transpire less and individual trees with less conductive xylem tissue (i.e., sapwood). Both hypotheses held. At salinity concentrations ranging from fresh to 3 psu, forest structural changes alone resulted in stand water use reductions from 494 mm year-1 in freshwater stands to 316 mm year-1 in stands of slightly higher salinity. Tree sapwood function (inferred from radial sap flux profiles) also changed along this gradient and reduced sap flow rates by an additional 13.3% per unit increase in salinity (psu). Thus, stand water use was further reduced to 190 mm year-1 on saline sites. We found that forest structure is not the only change that affects water use in salinized watersheds; individual tree eco-physiological responses to salinity, manifesting in different radial sap flow profiles, are important as well.

中文翻译：

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盐度的小梯度对淡水湿地森林中的静水利用有很大影响

摘要 盐度入侵是造成全球淡水湿地流域变化的原因，但关于盐度小幅增加如何影响湿地水收支平衡知之甚少。我们研究了美国南卡罗来纳州的一片森林湿地，并在沿盐度梯度的 72 棵树/灌木上安装了液流探头。研究的物种包括树木 baldcypress (Taxodium distichum [L.] Rich.)、water tupelo (Nyssa Aquatica L.)、沼泽 tupelo (Nyssa biflora Walt.) 和灌木蜡桃 (Morella cerifera (L.) Small)。该研究通过增加对沿盐度梯度的树木/灌木的测量，改进了过去对温室幼苗研究的依赖，并更好地描述了低盐度对淡水湿地森林用水的作用。我们测量了与盐度、大气条件和季节相关的用水模式，并假设盐度会通过两种机制影响湿地森林用水：盐度干扰会产生具有较少蒸腾作用的物种和大小等级的林分和具有较少导电木质部组织（即边材）的个体树木。两个假设都成立。在盐度浓度从新鲜到 3 psu 的范围内，仅森林结构变化就导致淡水林分 1 年的 494 毫米减少到盐度稍高的林分 1 年的 316 毫米。树边材函数（从径向树液通量分布推断）也沿该梯度发生变化，并且每单位盐度 (psu) 增加，树液流速降低 13.3%。因此，咸水场地的积水使用量进一步减少到第 1 年 190 毫米。我们发现，森林结构并不是影响盐渍化流域用水的唯一变化；个体树木对盐度的生态生理反应，表现为不同的径向树液流剖面，也很重要。