Vegetation establishment, growth and succession in riparian ecosystems are linked to river flow dynamics and groundwater table fluctuations. This is especially true in Alpine gravel‐bed rivers with wide floodplains, geomorphically active floods and a strong river‐aquifer exchange. The role of short‐term groundwater fluctuations is not always clear in these ecosystems, as it is assumed that phreatophytic vegetation close to rivers is adapted to such conditions. Here, we provide data evidence of riparian plant response to short‐term groundwater table fluctuations in a braided gravel‐bed river (Maggia). We used indirect physiological variables for photosynthesis and transpiration—stomatal conductance g_s and daily variation in stem diameter ΔD_d—which we measured at six mature riparian trees of the Salicaceae family at two sites with different mean depths to groundwater during two growing seasons. The data demonstrate that (a) short‐term variation of the groundwater table affects riparian vegetation—at the site with deeper groundwater, the water table depth was the best predictor of g_s variability, while at the site with shallower groundwater, temperature and vapour pressure deficit (VPD) were the best predictors of ΔD_d variability; (b) instantaneous stomatal conductance is related to VPD, but conditioned by groundwater levels, with higher stomatal conductance for the same radiative input and VPD when the water table was higher for all trees; and (c) local microclimate measured at tree locations had a stronger predictive power for g_s than valley scale climate, suggesting local climate controls on vegetated stands on gravel bars. Our results provide evidence of riparian trees undertaking physiological adjustments to transpiration in response to groundwater stage, depending on their riparian floodplain setting.

中文翻译：

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砾石河中河岸植被对地下水位的响应的现场证据

河岸生态系统中的植被建立，生长和演替与河流流量动态和地下水位波动有关。在宽泛的洪泛区，地貌活跃的洪水和旺盛的蓄水层交换的高山砾石河中尤其如此。在这些生态系统中，地下水短期波动的作用并不总是很清楚，因为人们认为靠近河流的草皮植物适应了这种条件。在这里，我们提供了辫状砾石床河（Maggia）中河岸植物对短期地下水位波动的响应的数据证据。我们用于光合作用和间接生理变量蒸腾-气孔导度克_小号和茎直径日变化Δ d _d-我们在两个生长季节中，在两个位置处的洋柳科的六棵成熟河岸树上进行了测量，这两个树的地下水平均深度不同。数据表明：（a）地下水位的短期变化会影响河岸植被-在地下水较深的地方，地下水位深度是g _s变异性的最佳预测指标，而在地下水，温度和蒸汽较浅的地方压亏缺（V P d）为的最佳预测Δ d _d变性; （b）瞬时气孔导度与V P D有关，但受地下水位的影响，在所有树木的地下水位都较高的情况下，对于相同的辐射输入和V P D，气孔导度较高；（c）在树木位置测得的局部微气候对g _s的预测能力强于山谷规模的气候，这表明对砾石带植被的林地进行了局部气候控制。我们的结果提供了证据，表明河岸树木根据河岸泛滥平原的设置对地下水阶段进行蒸腾作用的生理调节。