Snyder Keirith A, Morrow Amira C, Stringham Tamzen K, Allen Scott T
Great Basin Rangelands Research Unit, USDA-ARS, 920 Valley Rd, Reno, NV 89512, USA.
Department of Agriculture, Veterinary and Rangeland Sciences, University of Nevada, Reno, 1664 North Virginia Street, Reno, NV 89557, USA.
Tree Physiol. 2024 Dec 16;44(12). doi: 10.1093/treephys/tpae143.
It has been postulated that stemflow, precipitation that flows from plant crowns down along branches and stems to soils, benefits plants that generate it because it increases plant-available soil water near the base of the plant; however, little direct evidence supports this postulation. Were plants' crowns to preferentially route water to their roots, woody plants with large canopies could benefit. For example, piñon and juniper tree encroachment into sagebrush steppe ecosystems could be facilitated by intercepted precipitation routed to tree roots as stemflow, hypothetically reducing water available for shrubs and grasses. We tested whether Great Basin piñon and juniper trees use and benefit from stemflow. In a drier-than-average and wetter-than-average water year, isotopically labeled water was applied to tree stems to simulate stemflow. Both species took up stemflow, with label signals peaking and receding over 2-4 days. Despite this uptake, no alleviation of water stress was detected in the drier year. The stemflow uptake resulted in some water stress alleviation in the wetter year, specifically for piñons, which took up water from deeper in the soil profile than did junipers. Mixing model analyses suggested that stemflow was a small fraction of the water in stems (⁓0-2%), but an order-of-magnitude larger fraction of the stemflow was transpired in those few days after addition. These findings represent a novel demonstration of the rapid uptake and use of stemflow that infiltrates the rhizosphere, but they also prompt questions about the remaining stemflow's fate and why alleviation of water stress was so minor.
有一种假说认为，茎流（即从植物树冠沿树枝和树干向下流到土壤的降水）对产生茎流的植物有益，因为它增加了植物基部附近土壤中可供植物利用的水分；然而，几乎没有直接证据支持这一假说。如果植物的树冠能优先将水分输送到根部，那么树冠较大的木本植物可能会从中受益。例如，矮松和杜松侵入蒿属草原生态系统可能会因截留的降水以茎流的形式输送到树木根部而得到促进，据推测这会减少可供灌木和草本植物利用的水分。我们测试了大盆地矮松和杜松是否利用茎流并从中受益。在一个比平均水平更干燥和更湿润的水年里，将同位素标记的水施加到树干上以模拟茎流。两个物种都吸收了茎流，标记信号在2 - 4天内达到峰值并消退。尽管有这种吸收，但在较干燥的年份中未检测到水分胁迫的缓解。在较湿润的年份中，茎流的吸收确实导致了一些水分胁迫的缓解，特别是对于矮松来说，它们从土壤剖面中比杜松更深的位置吸收水分。混合模型分析表明，茎流在茎中的水分中占比很小（约0 - 2%），但在添加后的几天内，茎流中被蒸腾的部分要大一个数量级。这些发现首次证明了渗入根际的茎流能被快速吸收和利用，但它们也引发了关于其余茎流去向以及为何水分胁迫缓解如此轻微的问题。
