Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033, Japan.
Department of Forest Science, Graduate School of Life and Environmental Sciences, Kyoto Prefectural University, 1-5 Shimogamohangi-cho, Sakyo, Kyoto, 606-8522, Japan.
Am J Bot. 2021 Oct;108(10):1932-1945. doi: 10.1002/ajb2.1753. Epub 2021 Oct 17.
The hydraulic architecture in the leaves, stems and roots of plants constrains water transport and carbon gain through stomatal limitation to CO absorption. Because roots are the main bottleneck in water transport for a range of plant species, we assessed the ecophysiological mechanism and importance of a high fraction of root hydraulic resistance in woody and herbaceous species.
Biomass partitioning and hydraulic conductance of leaves, stems, and roots of Japanese knotweed (Fallopia japonica, a perennial herb) and Japanese zelkova (Zelkova serrata, a deciduous tall tree) were measured. Theoretical analyses were used to examine whether the measured hydraulic architecture and biomass partitioning maximized the plant photosynthetic rate (the product of leaf area and photosynthetic rate per leaf area).
Root hydraulic resistance accounted for 83% and 68% of the total plant resistance for Japanese knotweed and Japanese zelkova, respectively. Comparisons of hydraulic and biomass partitioning revealed that high root-resistance fractions were attributable to low biomass partitioning to root organs rather than high mass-specific root conductance. The measured partitioning of hydraulic resistance closely corresponded to the predicted optimal partitioning, maximizing the plant photosynthetic rate for the two species. The high fraction of root resistance was predicted to be optimal with variations in air humidity and soil water potential.
These results suggest that the hydraulic architecture of plants growing in mesic and fertile habitats not only results in high root resistance due to small biomass partitioning to root organs, but contributes to efficient carbon gain.
植物叶片、茎和根中的水力结构限制了通过气孔限制的水分运输和碳吸收，从而限制了 CO2 的吸收。由于根系是多种植物水分运输的主要瓶颈，因此我们评估了高比例根水力阻力在木本和草本植物中的生态生理机制和重要性。
测量了日本葛藤（多年生草本植物）和日本榉木（落叶高大乔木）叶片、茎和根的生物量分配和水力导度。理论分析用于检验所测量的水力结构和生物量分配是否最大限度地提高了植物的光合速率（叶面积与单位叶面积光合速率的乘积）。
日本葛藤和日本榉木的总植物阻力中，根水力阻力分别占 83%和 68%。水力和生物量分配的比较表明，高根阻力分数归因于根系器官的生物量分配较低，而不是质量比根导较高。所测量的水力阻力分配与预测的最佳分配密切对应，最大限度地提高了两种植物的光合速率。高比例的根阻力被预测为在空气湿度和土壤水势变化时是最佳的。
这些结果表明，在湿润和肥沃生境中生长的植物的水力结构不仅由于根系器官的生物量分配较小而导致高根阻力，而且有助于有效的碳获取。
