United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan.
Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan.
Sci Total Environ. 2023 Aug 25;888:164005. doi: 10.1016/j.scitotenv.2023.164005. Epub 2023 May 16.
The amount of ozone absorbed by the tree leaves is a critical factor determining the ozone effects on forest trees. Stomatal ozone uptake of a forest canopy can be estimated from the ozone concentration and canopy conductance (g) determined by the sap-flow-based method. This method measures sap flow as a metric of crown transpiration and then derives g. The thermal dissipation method (TDM) has been used to measure sap flow in most studies adopting this approach. However, recent studies have indicated that TDM may underestimate sap flow, especially in ring-porous tree species. In the present study, the accumulated stomatal ozone uptake (AF) of a stand of Quercus serrata, a typical ring-porous tree species in Japan, was estimated by measuring sap flow using species-specific calibrated TDM sensors. Laboratory calibration of the TDM sensors revealed that the parameters (α and β) in an equation converting outputs from the sensors (K) to sap flux density (F) were substantially larger for Q. serrata than those originally proposed by Granier (1987). The F measured in the Q. serrata stand using calibrated TDM sensors were significantly larger than those obtained using non-calibrated sensors. The diurnal average of g and daytime AF (10.4 mm s and 10.96 mmol O m month) of the Q. serrata stand estimated by using calibrated TDM sensors in August 2020 were similar to those of forests dominated by Quercus species estimated by micrometeorological measurements in previous studies. In contrast, the g and daytime AF of the Q. serrata stand estimated by non-calibrated TDM sensors were remarkably lower than those estimated by micrometeorological measurements in previous studies, indicating severe underestimation. Therefore, it is strongly recommended that sap flow sensors are species-specifically calibrated when estimating the canopy conductance and ozone uptake of forests dominated by ring-porous trees based on sap flow measurements using TDM.
树叶吸收的臭氧量是决定臭氧对森林树木影响的关键因素。森林冠层的臭氧通过气孔吸收量可以根据基于 sap-flow 的方法确定的臭氧浓度和冠层导度 (g) 进行估算。该方法通过测量 sap 流作为树冠蒸腾的度量标准，然后推导出 g。热耗散方法（TDM）已被用于测量大多数采用这种方法的研究中的 sap 流。然而，最近的研究表明，TDM 可能会低估 sap 流，尤其是在环孔树种中。在本研究中，使用特定于物种的校准 TDM 传感器测量 sap 流，估算了日本典型环孔树种麻栎林分的累积气孔臭氧吸收量 (AF)。TDM 传感器的实验室校准表明，将传感器输出 (K) 转换为 sap 通量密度 (F) 的方程中的参数 (α 和 β) 对于 Q. serrata 比 Granier（1987 年）最初提出的要大得多。使用校准的 TDM 传感器测量的 Q. serrata 林分中的 F 明显大于使用未校准传感器获得的 F。2020 年 8 月，使用校准的 TDM 传感器估算的 Q. serrata 林分的 g 和白天的 AF（10.4mm s 和 10.96mmol O m 月）的日平均值与以前的研究中使用微气象测量法估算的以栎属为主的森林的平均值相似。相比之下，使用未校准的 TDM 传感器估算的 Q. serrata 林分的 g 和白天的 AF 明显低于以前的研究中使用微气象测量法估算的值，表明严重低估。因此，强烈建议在使用 TDM 基于 sap-flow 测量估算以环孔树为主的森林的冠层导度和臭氧吸收量时，对 sap 流传感器进行特定于物种的校准。
