2025-08-29 中国科学院（CAS）
中国科学院西双版納熱帯植物園の陳亜軍研究員らは、世界的に広く使われている樹木の樹液流量測定法「Granier型熱消散法（TDM）」に重大な欠陥があることを明らかにした。TDMは原理が単純で低コストなため普及しているが、従来の校正係数では特に木部導管が大きく水輸送能力の高い樹種（ツル植物や環孔材樹種）で流量を大幅に過小評価してしまう。本研究では拡散孔材18種、環孔材2種、ヤシ科6種、ツル植物5種を含む31種の木本植物を対象に系統的な再校正を実施し、係数（スケーリング因子と指数）が種ごとに大きく異なり、特に導管内腔面積比や比水力伝導度といった木部解剖学的特性に強く依存することを示した。さらに、統計モデルの設定や校正時の最大加圧条件も係数の精度に影響を与えることが判明した。ゴム農園で新しい係数を適用した結果、従来のモデルが群集レベルの蒸散量を過小評価していたことが確認され、改良パラメータでより現実的な推定が可能となった。研究者らは、樹木の水利用を正確に評価するには、種特異的な係数を導入し、単一センサーから森林全体へ拡張する際の不確実性も考慮すべきだと強調している。
＜関連情報＞
- https://english.cas.cn/newsroom/research_news/life/202509/t20250901_1051702.shtml
- https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.70488
広く用いられる熱放散樹液流量測定法における水理学的伝導度による系統的パラメータ変動 Hydraulic conductivity-induced systematic parameter variation in a widely used thermal dissipation sap-flow technique
Ya-Jun Chen, Phisamai Maenpuen, Masatoshi Katabuchi, Pantana Tor-ngern, Sari Palmroth, Shu-Bin Zhang, Yun-Xue Xiao, Meng Liu, Ram Oren
New Phytologist Published: 25 August 2025
DOI:https://doi.org/10.1111/nph.70488
Summary
- The Granier-type thermal-dissipation method (TDM) is the most widely used sap-flow technique. However, its original calibration coefficients often underestimate high flow rates, limiting their generality.
- We derived TDM coefficients (scaling factors and exponents) for 31 species, including 18 diffuse-porous, two ring-porous, six palms, and five lianas, representing a broad range of wood properties. Factors influencing the coefficients and their accuracy were also investigated. Furthermore, we compiled 119 published coefficients for 88 additional species covering seven major xylem types.
- Most recalibrated and published coefficient values were substantially different from the original values, particularly in ring-porous and liana species with high hydraulic conductivity. The coefficient values depend on the statistical models and the applied maximum pressure during the calibration process. Vessel–lumen area fraction and hydraulic conductivity explained the interspecific variation in two coefficients at both segment and species levels. We applied recalibrated and original coefficients to a rubber plantation and found that the original coefficients produced unreasonably low transpiration estimates, while recalibrated coefficients yielded reasonable values. Uncertainties in scaling processes, including sapwood-area and radial and azimuth effects, also contributed significantly to the overall estimates.
- Our study demonstrates that accurate transpiration estimation must also address scaling-related sources of variation, as they contribute equally to uncertainty as poor calibration.
