McCarthy Christopher, Bourbia Ibrahim, Brodribb Timothy
School of Natural Sciences, University of Tasmania, Private Bag 55, Tas, Hobart 7001 Tasmania, Australia.
Plant Physiol. 2025 Apr 30;198(1). doi: 10.1093/plphys/kiaf116.
High rates of photosynthesis require abundant water delivered to the canopy to replace water lost to transpiration. In addition to water drawn immediately from the soil, stem capacitance has been identified as an additional water source, particularly during transient transpiration states. However, little information is available about the potential of roots to contribute to plant capacitance because methodological constraints have made it challenging to quantify root capacitance. In this study, we present a method to measure the water storage capacity of the root system and assess its contribution to daytime transpiration. We used an optical dendrometer to obtain in situ measurements of water potential and transpiration in 2 contrasting conifer species, Oyster Bay pine (Callitris rhomboidea) and Monterey pine (Pinus radiata), allowing us to quantify diurnal changes in plant water deficit. We employed a modified flow meter to gauge the rehydration kinetics of the below-ground and above-ground systems separately. We observed that root capacitance is a major supplier to the water demands during transient changes in transpiration for both species. Notably, the total below-ground capacitance exceeded the above-ground capacitance in C. rhomboidea, while the 2 capacitances were similar in P. radiata. Our findings highlight the importance of measuring and including below-ground capacitance in hydraulic models to accurately predict diurnal plant water status and stomatal behavior.
高光合速率需要向树冠输送大量水分，以补充因蒸腾作用而损失的水分。除了直接从土壤中汲取的水分外，茎干持水力已被确认为另一种水源，尤其是在短暂的蒸腾状态期间。然而，关于根系对植物持水力的潜在贡献的信息很少，因为方法上的限制使得量化根系持水力具有挑战性。在本研究中，我们提出了一种测量根系储水能力并评估其对白天蒸腾作用贡献的方法。我们使用光学测树仪原位测量了两种对比针叶树物种——牡蛎湾松（Callitris rhomboidea）和辐射松（Pinus radiata）的水势和蒸腾作用，从而能够量化植物水分亏缺的日变化。我们采用了一种改良的流量计分别测量地下和地上系统的再水化动力学。我们观察到，对于这两个物种，根系持水力在蒸腾作用的瞬态变化期间都是水分需求的主要供应源。值得注意的是，在牡蛎湾松中，地下总持水力超过地上持水力，而在辐射松中，这两种持水力相似。我们的研究结果强调了在水力模型中测量并纳入地下持水力对于准确预测植物日水分状况和气孔行为的重要性。
