Abstract Stem water content (θ) is an important state variable in the soil-plant-atmosphere continuum (SPAC), and varies temporally and spatially in response to environmental factors and plant growth stages. However, it is difficult to measure θ distribution in living trees in a manner that is not destructive. In this study, temporal and spatial variations in θ within living tree stems were examined based on minimally destructive electrical resistivity tomography. Measurements of tree bulk electrical resistivity (ρ), stem temperature, sap flow and stem water potential were taken on an Australian native tree species, Allocasuarina verticillata. The results show that θ estimated from adjusted resistivity (ρ*) based on a reference ρ-θ relationship approach agrees well with θ estimated from predawn stem water potential. Sapwood θ gradually increased during the wet season and substantially decreased during the dry season as predawn stem water potential and sap velocity increased and decreased, respectively, and ρ*-estimated θ reveals water replenishment and loss within the sapwood during the wet and dry seasons, respectively. During the dry period, mean sapwood θ for the study trees decreased to 0.23 cm3/cm3 (January), and daily maximum sap velocity was only about 10 % of that in wet season, suggesting that the trees were suffering heavy water stress. The spatially exhaustive method to estimate stem water content within living trees proposed here provides an additional approach to investigating tree response to water stress.

中文翻译：

---

电阻率层析成像测定的活树茎内含水量的时空变化

摘要 茎含水量（θ）是土壤-植物-大气连续体（SPAC）中的一个重要状态变量，随着环境因素和植物生长阶段的变化而发生时空变化。然而，很难以非破坏性的方式测量活树中的 θ 分布。在这项研究中，基于最小破坏性电阻率断层扫描检查了活树茎内 θ 的时间和空间变化。对澳大利亚本土树种 Allocasuarina verticillata 进行了树木体积电阻率 (ρ)、茎温、树液流量和茎水势的测量。结果表明，从基于参考 ρ-θ 关系方法的调整电阻率 (ρ*) 估计的 θ 与从黎明前茎水势估计的 θ 非常吻合。随着黎明前茎水势和树液流速的增加和减少，边材 θ 在雨季逐渐增加，在旱季显着下降，ρ* 估计的 θ 揭示了干湿季节边材内的水分补充和损失，分别。在枯水期，研究树木的平均边材θ 下降到0.23 cm3/cm3（1 月），日最大树液速度仅为雨季的10% 左右，表明树木正遭受严重的水分胁迫。这里提出的估算活树中茎水分含量的空间详尽方法提供了一种额外的方法来研究树木对水分胁迫的反应。