Observations of stem water storage in trees of opposing hydraulic strategies
Observations of stem water storage in trees of opposing hydraulic strategies
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DOI：
10.1890/es15-00170.1
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发表时间：
2015-09-01
期刊：
影响因子：
2.7
通讯作者：
Vogel, Christoph S.
中科院分区：
文献类型：
--
作者：
Matheny, Ashley M.;Bohrer, Gil;Vogel, Christoph S.
水力电容和储水形成了防止木质部系统内空化和电导率损失的关键缓冲器。叶、枝、茎和根中储存的水分的排出会显着影响液流、气孔导度和蒸腾作用。储存量根据土壤水的可用性、树木大小、木材解剖结构和密度、耐旱性和水力策略（不等水或等水）而有所不同。然而，大多数研究都集中在针叶树或热带树种储存量的测量上。我们展示了一种使用频域反射计 (FDR) 的新颖方法，可以连续、直接测量密歇根州森林中两种硬木树种的木材水分含量。我们展示了为期两个月的研究结果，比较了成熟红橡树和红枫树这两种木材密度、水力结构和水力策略不同的树种之间的蓄水动态。我们还包括与使用不同探头长度仅对红橡木中活性边材、整个导电边材和心材外部部分的水含量进行采样有关的结果。研究的两个物种都表现出昼夜储存周期，与树液通量的动态非常吻合。红枫是一种散孔、相对等水的树种，在潮湿和干燥时期都表现出对储存水的强烈依赖。红橡树是一种环孔相对不等水的树种，对储存的依赖较小，并且没有表现出对土壤水势的依赖。橡树中的长 FDR 探针和短 FDR 探针之间的比较表明，当土壤湿度条件受到限制时，橡树可以利用木质部最内层中储存的水。我们发现 FDR 探头是一种可靠、实用的方法，可快速连续自动测量硬木中的木材水分含量。应用 FDR 技术测量树木储水量将使森林生态学家和建模界受益，因为我们可以提高对大规模植物水动力过程的理解和模拟。
Hydraulic capacitance and water storage form a critical buffer against cavitation and loss of conductivity within the xylem system. Withdrawal from water storage in leaves, branches, stems, and roots significantly impacts sap flow, stomatal conductance, and transpiration. Storage quantities differ based on soil water availability, tree size, wood anatomy and density, drought tolerance, and hydraulic strategy (anisohydric or isohydric). However, the majority of studies focus on the measurement of storage in conifers or tropical tree species. We demonstrate a novel methodology using frequency domain reflectometry (FDR) to make continuous, direct measurements of wood water content in two hardwood species in a forest in Michigan. We present results of a two month study comparing the water storage dynamics between a mature red oak and red maple, two species with differing wood densities, hydraulic architecture, and hydraulic strategy. We also include results pertaining to the use of different probe lengths to sample water content only within the active sapwood and over the entire conductive sapwood and the outer portion of heartwood in red oak. Both species studied exhibited diurnal cycles of storage that aligned well with the dynamics of sap flux. Red maple, a diffuse porous, relatively isohydric species showed a strong dependence on stored water during both wet and dry periods. Red oak, a ring porous relatively anisohydric species, was less reliant on storage, and did not demonstrate a dependence on soil water potential. Comparison between long and short FDR probes in the oak revealed that oaks may utilize water stored in the innermost layers of the xylem when soil moisture conditions are limiting. We found the FDR probes to be a reliable, functional means for continuous automated measurement of wood water content in hardwoods at a fast time scale. Application of FDR technology for the measurement of tree water storage will benefit forest ecologists as well as the modeling community as we improve our understanding and simulations of plant hydrodynamic processes on a large scale.