利用光化學反射指數推估在高、低海生長之台灣二葉松在不同季節之光合作用效率

Using Photochemical Reflectance Index to Estimate Photosynthetic Light-Use Efficiency of Pinus taiwanensis in High and Low Elevation in Different Seasons

本研究以台灣廣範圍海拔分布，且具純林之主要針葉樹種–台灣二葉松（Pinus taiwanensisHay.）為對象，探討在不同季節及海拔塔塔加（約2,600 m）及惠蓀林場（約800 m）之光合作用光利用效率[photosynthetic light-use efficiency, LUE = 光合速率/光合光子流密度（photosynthetic photonflux density, PPFD）]與葉片反射光譜[光化學反射指數（photochemical reflectance index, PRI）, =（R531-R570）/ （R531+R570）]之關係，以開發簡單、迅速、有效且能用於不同海拔植物之同化能力評估及監測技術。結果顯示，PRI及LUE均會隨光度（PPFD）之增加及溫度之下降而降低。在光度相同之情況下，將在不同季節及海拔所測得之資料合併分析時，LUE與PRI間呈顯著之正相關，兩者間迴歸方程式之截距及斜率各與PPFD呈顯著之曲線負相關。經複迴歸分析可得到方程式，即：LUE = 6.505 – 1.470•ln（PPFD） + 0.084•[ln（PPFD）]2 + 70.606•PRI – 16.696•ln（PPFD）•PRI +0.996•[ln（PPFD）]2•PRI, （r2 = 0.910, P<0.001）。將實測之PPFD與PRI代入上式中，便可得LUE之推估值。經單相關迴歸分析發現此推估值與實測值間呈極顯著之直線正相關，其判斷係數數（r2）高達0.912（P<0.001），而且迴歸方程式也接近X=Y，故可利用上述方程式並以容易測得之PPFD與PRI來推估台灣二葉松在不同海拔、季節及光度下之光合效率變化。

We investigated the relationship between photosynthetic light-use efficiency [LUE, = (photosynthetic rate) / (photosynthetic photon flux density, PPFD)] and the photochemical reflectance index [PRI, = (R531 - R570)/(R531- R570)] of pine needles (Pinus taiwanensis Hay.) under different PPFD at high (2,600 m a.s.l) and low-elevation (800 m a.s.l) sites through different seasons. Results indicate that both PRI and LUE decreased with the increasing of PPFD and the decreasing of temperature. When data obtained at different elevations and seasons were pooled for analysis, at a given level of illumination, LUE always showed a significant positive correlation with PRI. Because both the intercept and slope of LUE–PRI equation showed a negative regression with PPFD, an empirical regression model, i.e. LUE = 6.505 - 1.470˙ln(PPFD) + 0.084˙[ln(PPFD)]^2 + 70.606˙PRI - 16.696˙ln(PPFD)˙PRI + 0.996˙[ln(PPFD)]^2˙PRI, can be appropriate for multiple regression analysis (r^2 = 0.910, P＜0.001). Based on the close correlation between the estimated and measured LUE (Y = 1.001˙X - 0.002, r^2 = 0.912, P＜0001), we conclude this empirical regression model can be used to simulate the seasonal and diurnal variations of LUE for P. taiwanensis under varied PPFD grown at high- and low-elevation sites.