Bauerle T L, Richards J H, Smart D R, Eissenstat D M
Department of Horticulture, The Pennsylvania State University, University Park, PA 16802, USA.
Plant Cell Environ. 2008 Feb;31(2):177-86. doi: 10.1111/j.1365-3040.2007.01749.x. Epub 2007 Nov 20.
Redistribution of water within plants could mitigate drought stress of roots in zones of low soil moisture. Plant internal redistribution of water from regions of high soil moisture to roots in dry soil occurs during periods of low evaporative demand. Using minirhizotrons, we observed similar lifespans of roots in wet and dry soil for the grapevine 'Merlot' (Vitis vinifera) on the rootstock 101-14 Millardet de Gramanet (Vitis riparia x Vitis rupestris) in a Napa County, California vineyard. We hypothesized that hydraulic redistribution would prevent an appreciable reduction in root water potential and would contribute to prolonged root survivorship in dry soil zones. In a greenhouse study that tested this hypothesis, grapevine root systems were divided using split pots and were grown for 6 months. With thermocouple psychrometers, we measured water potentials of roots of the same plant in both wet and dry soil under three treatments: control (C), 24 h light + supplemental water (LW) and 24 h light only (L). Similar to the field results, roots in the dry side of split pots had similar survivorship as roots in the wet side of the split pots (P = 0.136) in the C treatment. In contrast, reduced root survivorship was directly associated with plants in which hydraulic redistribution was experimentally reduced by 24 h light. Dry-side roots of plants in the LW treatment lived half as long as the roots in the wet soil despite being provided with supplemental water (P < 0.0004). Additionally, pre-dawn water potentials of roots in dry soil under 24 h of illumination (L and LW) exhibited values nearly twice as negative as those of C plants (P = 0.034). Estimates of root membrane integrity using electrolyte leakage were consistent with patterns of root survivorship. Plants in which nocturnal hydraulic redistribution was reduced exhibited more than twice the amount of electrolyte leakage in dry roots compared to those in wet soil of the same plant. Our study demonstrates that besides a number of ecological advantages to protecting tissues against desiccation, internal hydraulic redistribution of water is a mechanism consistent with extended root survivorship in dry soils.
植物体内水分的重新分配可以减轻土壤湿度低的区域中根系的干旱胁迫。在蒸发需求较低的时期，植物会将土壤湿度高的区域的水分重新分配到干旱土壤中的根系。使用微型根窗，我们观察到在加利福尼亚州纳帕县的一个葡萄园里，葡萄品种“梅洛”（欧亚种葡萄）嫁接到砧木101-14 米勒德·德格拉马内（河岸葡萄×沙地葡萄）上后，其在湿润和干旱土壤中的根系寿命相似。我们推测水力再分配可以防止根水势显著降低，并有助于延长干旱土壤区域中根系的存活时间。在一项验证这一推测的温室研究中，葡萄根系使用分隔花盆进行分隔，并生长6个月。我们使用热电偶湿度计，在三种处理方式下测量了同一植株在湿润和干旱土壤中的根水势：对照（C）、24小时光照+补充水分（LW）和仅24小时光照（L）。与田间结果相似，在C处理中，分隔花盆干旱一侧的根系存活情况与湿润一侧的根系相似（P = 0.136）。相比之下，根系存活减少与通过24小时光照实验性减少水力再分配的植株直接相关。尽管LW处理的植株被提供了补充水分，但其干旱一侧的根系寿命只有湿润土壤中根系的一半（P < 0.0004）。此外，在24小时光照（L和LW）下，干旱土壤中根系的黎明前水势显示出的值几乎是C组植株的两倍负值（P = 0.034）。使用电解质渗漏来估计根膜完整性与根系存活模式一致。与同一植株湿润土壤中的根系相比，夜间水力再分配减少的植株干旱根系中的电解质渗漏量多出两倍以上。我们的研究表明，除了在保护组织免受干燥方面具有许多生态优势外，水分的内部水力再分配是一种与干旱土壤中根系延长存活时间相一致的机制。
