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Responses of sap flow, leaf gas exchange and growth of hybrid aspen to elevated atmospheric humidity under field conditions

机译：田间条件下汁液流量，叶片气体交换和杂种白杨生长对大气湿度升高的响应

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An increase in average air temperature and frequency of rain events is predicted for higher latitudes by the end of the 21st century, accompanied by a probable rise in air humidity. We currently lack knowledge on how forest trees acclimate to rising air humidity in temperate climates. We analysed the leaf gas exchange, sap flow and growth characteristics of hybrid aspen (Populus tremula × P. tremuloides) trees growing at ambient and artificially elevated air humidity in an experimental forest plantation situated in the hemiboreal vegetation zone. Humidification manipulation did not affect the photosynthetic capacity of plants, but did affect stomatal responses: trees growing at elevated air humidity had higher stomatal conductance at saturating photosynthetically active radiation (gs sat) and lower intrinsic water-use efficiency (IWUE). Reduced stomatal limitation of photosynthesis in trees grown at elevated air humidity allowed slightly higher net photosynthesis and relative current-year height increments than in trees at ambient air humidity. Tree responses suggest a mitigating effect of higher air humidity on trees under mild water stress. At the same time, trees at higher air humidity demonstrated a reduced sensitivity of IWUE to factors inducing stomatal closure and a steeper decline in canopy conductance in response to water deficit, implying higher dehydration risk. Despite the mitigating impact of increased air humidity under moderate drought, a future rise in atmospheric humidity at high latitudes may be disadvantageous for trees during weather extremes and represents a potential threat in hemiboreal forest ecosystems.
机译：预计到21世纪末，较高纬度的平均气温和降雨事件的频率将增加，同时空气湿度可能会上升。目前，我们缺乏关于温带气候下林木如何适应空气湿度上升的知识。我们分析了在半自然植被区的一个实验性人工林中，在环境湿度和人工提高的空气湿度下生长的混合白杨（Populus tremula×P. tremuloides）树木的叶片气体交换，汁液流动和生长特性。增湿操作不会影响植物的光合能力，但会影响气孔响应：在空气湿度较高的情况下生长的树木在饱和光合有效辐射（g sat ）时具有较高的气孔导度，而固有用水量较低。效率（IWUE）。与在环境空气湿度下的树木相比，在空气湿度较高的情况下生长的树木的光合作用气孔限制降低，从而使净光合作用和当前当年的相对高度增量略高。树木的反应表明，在轻度水分胁迫下，较高的空气湿度对树木的缓解作用。同时，空气湿度较高的树木表现出IWUE对导致气孔关闭的因素的敏感性降低，并且由于水分亏缺，冠层电导率急剧下降，这意味着更高的脱水风险。尽管在中等干旱条件下空气湿度增加有缓解的影响，但未来在高纬度地区大气湿度的上升可能会对极端天气期间的树木不利，并且对半实体森林生态系统构成潜在威胁。

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