Abstract Climate change is expected to increase the frequency of droughts in most tropical regions in the coming decades. A passive phenomenon called hydraulic redistribution (HR) allows some plant species to take up water from deep and wet soil layers and redistribute it in the upper dry layers where other plants and soil biota can benefit from it. In addition, soil fertilization, particularly potassium (K), may also affect drought-adaptive mechanisms and increase water use efficiency (WUE) on poor and acidic tropical soils. The present study aimed at quantifying the role of HR and K fertilization on both wood productivity and WUE for stemwood production (WUEp) of Eucalyptus grandis plantations in Brazil under ambient and reduced (−37%) throughfall conditions. Tree transpiration was measured using trunk sap flow sensors over 21 months, and HR was estimated from the reverse sap flow (RF) observed in shallow roots over 18 months. Tree biomass, hydraulic conductance, soil water storage from surface to the water table (down to 17 m), and leaf photosynthetic capacity were also assessed. Significant HR was detected over the whole year, even during the rainy seasons. Neither potassium fertilization nor throughfall exclusion affected the velocity of water transported by HR, probably because most trees reached water table. Nonetheless, some photosynthetic capacity parameters, including the maximum photosynthetic rate (Amax), increased in treatments with K addition. This higher Amax combined with an increased sapwood area index, was associated with an increase in water uptake by 30 %–50 % and WUEp by 300 % relative to K-deficient trees. We postulate that the increase in WUEp promoted by potassium fertilization was partly driven by an increase in biomass allocation to wood, at the expense of foraging organs (leaves and roots), because K addition alleviated constraints on light and water use. Our results indicate that fertilizing E. grandis plantations with K is beneficial to both wood biomass production and WUEp.

中文翻译：

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钾肥可提高大桉树人工林茎材生产的水力再分配和水分利用效率

摘要 未来几十年，气候变化预计将增加大多数热带地区的干旱频率。一种称为水力再分配 (HR) 的被动现象允许一些植物物种从深层和潮湿的土壤层吸收水分，并将其重新分配到上层干燥层，其他植物和土壤生物群可以从中受益。此外，土壤施肥，尤其是钾 (K)，也可能影响干旱和酸性热带土壤的干旱适应机制并提高水分利用效率 (WUE)。本研究旨在量化 HR 和 K 施肥对巴西大桉树人工林在环境和减少 (-37%) 贯穿条件下的木材生产力和 WUE 的作用。使用树干液流传感器在 21 个月内测量了树木蒸腾作用，HR 是根据 18 个月内在浅根中观察到的反向液流 (RF) 估算的。还评估了树木生物量、水力传导率、从地表到地下水位（低至 17 m）的土壤储水量和叶片光合能力。即使在雨季，全年也检测到显着的 HR。钾肥和落水排除都不会影响 HR 输送的水的速度，这可能是因为大多数树木都达到了地下水位。尽管如此，一些光合能力参数，包括最大光合速率（Amax），在添加钾的处理中增加。这种较高的 Amax 与增加的边材面积指数相结合，与缺钾树木的吸水量增加 30%–50% 和 WUEp 增加 300% 相关。我们假设钾肥促进 WUEp 的增加部分是由于生物量分配给木材的增加，以牺牲觅食器官（叶和根）为代价，因为钾的添加减轻了对光和水利用的限制。我们的结果表明，用 K 给 E. grandis 种植园施肥有利于木材生物量生产和 WUEp。