Department of Biological Sciences, Rutgers University Newark, NJ, USA.
Front Plant Sci. 2012 May 21;3:103. doi: 10.3389/fpls.2012.00103. eCollection 2012.
Sap flow measurements have become integral in many physiological and ecological investigations. A number of methods are used to estimate sap flow rates in trees, but probably the most popular is the thermal dissipation (TD) method because of its affordability, relatively low power consumption, and ease of use. However, there have been questions about the use of this method in ring-porous species and whether individual species and site calibrations are needed. We made concurrent measurements of sap flow rates using TD sensors and the tissue heat balance (THB) method in two oak species (Quercus prinus Willd. and Quercus velutina Lam.) and one pine (Pinus echinata Mill.). We also made concurrent measurements of sap flow rates using both 1 and 2-cm long TD sensors in both oak species. We found that both the TD and THB systems tended to match well in the pine individual, but sap flow rates were underestimated by 2-cm long TD sensors in five individuals of the two ring-porous oak species. Underestimations of 20-35% occurred in Q. prinus even when a "Clearwater" correction was applied to account for the shallowness of the sapwood depth relative to the sensor length and flow rates were underestimated by up to 50% in Q. velutina. Two centimeter long TD sensors also underestimated flow rates compared with 1-cm long sensors in Q. prinus, but only at large flow rates. When 2-cm long sensor data in Q. prinus were scaled using the regression with 1-cm long data, daily flow rates matched well with the rates measured by the THB system. Daily plot level transpiration estimated using TD sap flow rates and scaled 1 cm sensor data averaged about 15% lower than those estimated by the THB method. Therefore, these results suggest that 1-cm long sensors are appropriate in species with shallow sapwood, however more corrections may be necessary in ring-porous species.
树液流测量在许多生理和生态研究中已变得不可或缺。有许多方法可用于估计树木中的树液流速，但由于其价格合理、相对低功耗和易于使用，热消散（TD）方法可能是最受欢迎的方法。然而，人们对该方法在环孔材树种中的使用以及是否需要针对个别树种和地点进行校准提出了质疑。我们在两种橡树（Quercus prinus Willd. 和 Quercus velutina Lam.）和一种松树（Pinus echinata Mill.）中使用 TD 传感器和组织热平衡（THB）方法同时进行了树液流速的测量。我们还在这两种橡树中同时使用 1 厘米和 2 厘米长的 TD 传感器进行了树液流速的测量。我们发现，TD 和 THB 系统在松树个体中往往匹配良好，但在两个环孔材橡树个体中，2 厘米长的 TD 传感器低估了 5 个个体的树液流速。即使应用“Clearwater”校正以考虑相对于传感器长度的边材深度较浅，也会导致 Q. prinus 的低估率达到 20-35%，而在 Q. velutina 中，低估率甚至高达 50%。在 Q. prinus 中，2 厘米长的 TD 传感器与 1 厘米长的传感器相比也低估了流速，但仅在大流速下才会低估。当 Q. prinus 中 2 厘米长传感器的数据通过与 1 厘米长数据的回归进行缩放时，每日流量与 THB 系统测量的流量非常吻合。使用 TD 树液流速率和缩放后的 1 厘米传感器数据估算的每日绘图水平蒸腾量平均比 THB 方法估算的蒸腾量低约 15%。因此，这些结果表明，在边材较浅的树种中，1 厘米长的传感器是合适的，但在环孔材树种中可能需要更多的校正。
