Department of Agricultural and Food Sciences, University of Bologna, Bologna, Italy.
Ann Bot. 2019 Oct 29;124(4):605-616. doi: 10.1093/aob/mcz001.
Giant reed (Arundo donax L.) is a deep-rooted crop that can survive prolonged dry periods probably as a result of its capacity to uptake water from below ground, but specific information on the functioning of deep/shallow roots is missing. The objective of this study was to understand the dynamic interrelationships of root water acquisition, canopy water conservation and abscisic acid (ABA) signals from both shallow and deep roots.
In transparent split top-bottom rhizotron systems (1-m-high columns), where hydraulically isolated and independently watered layers were created with the aid of calibrated soil moisture sensors, water uptake trends were monitored. Rooting patterns were traced on the walls of the rhizotrons. Leaf gas exchange was determined using a portable infrared gas analyser. Leaf and root ABA concentrations were monitored.
Under well-watered conditions, water uptake from both upper and deeper soil layers was similar. Water uptake from deeper soil layers increased gradually by up to 2.2-fold when drought stress was imposed to upper layers compared to the control conditions. Despite the significant increase in water uptake from deeper layers, surface root length density of drought-treated plants remained unchanged, suggesting increased root water uptake efficiency by these roots. However, these adjustments were not sufficient to sustain photosynthesis and therefore biomass accumulation, which was reduced by 42 %. The ABA content in shallower drought-treated roots increased 2.6-fold. This increase closely and positively correlated with foliar ABA concentration, increased intrinsic water use efficiency and leaf water potential (LWP).
Giant reed is able to change its water sources depending on water availability and to maximize water uptake efficiency to satisfy canopy evapotranspirative demands. The regulation of deep root functioning and distribution, adjustment of canopy size, and root/foliar synthesized ABA play a central role in controlling LWP and leaf transpiration efficiency.
巨蔺（Arundo donax L.）是一种深根作物，能够在长时间的干旱期存活，这可能是由于其从地下吸收水分的能力，但关于深/浅层根系功能的具体信息尚不清楚。本研究的目的是了解浅层和深层根系的根水分获取、冠层水分保持和脱落酸（ABA）信号之间的动态相互关系。
在透明的上下分体式根箱系统（1 米高的柱体）中，借助校准的土壤湿度传感器创建了水力隔离和独立浇水的分层，监测水分吸收趋势。在根箱壁上追踪根系模式。使用便携式红外气体分析仪测定叶片气体交换。监测叶片和根 ABA 浓度。
在充分供水条件下，上层和深层土壤的水分吸收量相似。与对照条件相比，上层干旱胁迫下，深层土壤的水分吸收量逐渐增加了 2.2 倍。尽管深层土壤水分吸收量显著增加，但干旱处理植物的表层根长密度保持不变，这表明这些根的根水分吸收效率提高。然而，这些调整不足以维持光合作用，因此生物量积累减少了 42%。浅层干旱处理根中的 ABA 含量增加了 2.6 倍。这种增加与叶片 ABA 浓度、内在水分利用效率和叶片水势（LWP）密切正相关。
巨蔺能够根据水分供应情况改变其水源，并最大限度地提高水分吸收效率，以满足冠层蒸腾需求。深根功能和分布的调节、冠层大小的调整以及根/叶合成的 ABA 在控制 LWP 和叶片蒸腾效率方面起着核心作用。
