Soil moisture heterogeneity in the root-zone is common during both the establishment of tree seedlings and in experiments aiming to impose semi-constant soil moisture deficits, but its effects on regulating plant water use compared to homogenous soil drying are not well known in trees. Pronounced vertical soil moisture heterogeneity was imposed on black poplar (Populus nigra L.) grown in soil columns by altering irrigation frequency, to test whether plant water use, hydraulic responses, root phytohormone concentrations, and root xylem sap chemical composition differed between wet (well-watered, WW), homogeneously (infrequent deficit irrigation, IDI) and heterogeneously dry soil (frequent deficit irrigation, FDI). At the same bulk soil water content, FDI plants had greater water use than IDI plants, probably because root abscisic acid (ABA) concentration was low in the upper wetter layer of FDI plants, which maintained root xylem sap ABA concentration at basal levels in contrast with IDI. Soil drying did not increase root xylem concentration of any other hormone. Nevertheless, plant-to-plant variation in xylem jasmonic acid (JA) concentration was negatively related to leaf stomatal conductance within WW and FDI plants. However, feeding detached leaves with high (1,200 nM) JA concentrations via the transpiration stream decreased transpiration only marginally. Xylem pH and sulphate concentration decreased in FDI plants compared to well-watered plants. Frequent deficit irrigation increased root accumulation of the cytokinin trans-zeatin (tZ), especially in the dry lower layer, and of the ethylene precursor ACC, in the wet upper soil layer. Root hormone accumulation might explain the maintenance of high root hydraulic conductance and water use in FDI plants (similar to well-watered plants) compared to IDI plants. In irrigated tree crops, growers could vary irrigation scheduling to control water use by altering the hormone balance.

中文翻译：

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土壤水分异质性通过改变根和木质部汁液植物激素浓度来调节黑杨的水分利用。

在树苗的建立和旨在施加半恒定土壤水分亏缺的实验中，根区的土壤水分异质性很常见，但是与均匀土壤干燥相比，它对调节植物水分利用的影响在树木中并不为人所知。通过改变灌溉频率，对生长在土壤柱中的黑杨（Populus nigra L.）施加明显的垂直土壤水分异质性，以测试植物水分利用，水力响应，根植物激素浓度和根木质部树液化学组成在湿（井）之间是否存在差异。 -浇水，WW），均质（不经常性缺水灌溉，IDI）和异质土壤（不经常性缺水灌溉，FDI）。在相同的土壤含水量下，FDI植物的用水量要高于IDI植物，可能是因为FDI植物的上部湿润层中的根脱落酸（ABA）浓度较低，与IDI相比，其将根部木质部汁液ABA的浓度保持在基础水平。土壤干燥不会增加任何其他激素的根木质部浓度。然而，在WW和FDI植物中，木质​​部茉莉酸（JA）浓度的植物间差异与叶片气孔导度负相关。但是，通过蒸腾流饲喂高（1,200 nM）JA浓度的离体叶片只能稍微减少蒸腾量。与灌溉良好的植物相比，FDI植物的木质部pH和硫酸盐浓度降低。频繁的亏水灌溉增加了细胞分裂素反玉米蛋白（tZ）的根积累，尤其是在干燥的下层，而乙烯前体ACC的根积累在湿的上层土壤。与IDI植物相比，FDI植物（类似于灌溉良好的植物）中根系激素的积累可能解释了高根水力传导和水的维持。在灌溉的木本作物中，种植者可以改变灌溉时间表以通过改变激素平衡来控制用水。