桉树液流径向变化及其对整树蒸腾估算的影响

倪隆康; 林芙蓉; 周翠鸣; 何文; 顾大形; 秦佳双

doi:10.13275/j.cnki.lykxyj.2022.006.019

桉树液流径向变化及其对整树蒸腾估算的影响

Radial Variation of Sap Flow in Eucalyptus and Its Effect on the Estimation of Whole Tree Transpiration

摘要

摘要:
目的分析液流密度径向差异及其对整树蒸腾量估算的影响，以期为中大径级桉树人工林蒸腾的准确估算和尺度扩展提供可靠依据。
方法采用Granier热扩散探针法(TDP)测定了10年生中等径级尾巨桉(Eucalyptus urophylla × Eucalyptus grandis)3个边材径向深度0～2、2～4、4～6 cm的液流密度。
结果尾巨桉液流密度径向分布格局为递减型，日变化格局均为单峰型。用单点径向深度0～2、2～4、4～6 cm液流密度代表整个边材液流密度估算的整树日蒸腾量T_r₂、T_r₄和T_r₆较基于多点估算值T_r₂₄₆分别高估92.9%、低估28.2%和低估74.0%。由于0～2 cm 边材深度液流密度对环境变化较为敏感，并且 T_r₂与T_r₂₄₆之间的拟合精度较高(R²=0.964)，因此，基于T_r₂构建的整树日蒸腾量估算校正函数T_r₂₄₆=0.522T_r₂有效的提高了整树蒸腾估算的便捷性和准确度。
结论中等径级尾巨桉液流密度具有明显的径向变化特征，不考虑这种径向变化将会导致整树蒸腾估算的较大误差。基于边材最外侧（0～2 cm）液流密度估算的整树蒸腾经过校正后可以方便准确地估算中等径级桉树人工林蒸腾耗水。

Abstract:
Objective To provide a reliable basis for the accurate estimation and scale expansion of transpiration in medium and large diameter Eucalyptus plantations, the radial variation of sap flow and its effect on the estimation of whole tree transpiration were analyzed.
MethodsThe sap flow density at three sapwood depths (0-2 cm, 2-4 cm and 4-6 cm) of 10-year-old Eucalyptus urophylla × Eucalyptus grandis was monitored using the Granier-type thermal dissipation probe (TDP).
Result The results showed that the diurnal variation of sap flow density in each sapwood depth showed a single-peak pattern, and the sap flow density decreased with the increase of sapwood depth. Compared with the daily whole tree transpiration estimated based on sap flow density in three sapwood depths (T_r₂₄₆), the daily transpiration when trade the sap flow density in 0-2 cm (T_r₂), 2-4 cm (T_r₄) and 4-6 cm (T_r₆) sapwood depth as the whole tree sap flow density were overestimated by 92.9% and underestimated by 28.2% and 74.0%, respectively. The sap flow in 0-2 cm sapwood depth was more sensitive to environment compared with the other two depths and Tr₂ had higher correlation with T_r₂₄₆(R²=0.964) compared with T_r₄ and T_r₆. As a result, the sap flow in 0-2 cm depth could be used to estimate whole tree transpiration of Eucalyptus when calibrated based on T_r₂₄₆(T_r₂₄₆=0.522 T_r₂).
Conclusion Eucalyptus shows obvious radial variation in sap flow density and there may lead to large errors in estimating whole tree transpiration when ignoring the radial variation of sap flow. The whole tree transpiration of Eucalyptus can be estimated easily and accurately using sap flow in 0-2 cm sapwood depth based on the calibrated function.

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