不同海拔及季節下台灣原生芒屬植物之光合作用能力與葉綠素含量及氣孔導度間關係

Photosynthetic capacity at high and low elevations in different seasons and the relationship between chlorophyll content and stomatal conductance: A Study of the Miscanthus species in sub-tropical Taiwan

Net photosynthetic rate (Pn) of Miscanthus leaves, with different chlorophyll content (Chl), was measured at high (natural habitat-grown M. transmorrisonensis and M. sinensis var. formosanus at 3,000 and 2,100 m a.s.l., respectively) and low (pot-grown M. floridulus at 70 m a.s.l.) elevations through different seasons. In the winter, even the leaf temperature (T) drops to 6 o C, the Pn of M. transmorrisonensis leaves (Chl ranged 0.17–0.46 g m–2 ) that were measured under the photosynthetic photon flux density (PPFD) of 1,200 μmol m–2 s –1 (denoted as P1200) could retain 0.4–3.2 μmol CO2 m–2 s –1 . While in the summer, the P1200 measured at 19o C could raise to 3.9–19.9 μmol CO2 m–2 s –1 . At low elevation, M. floridulus could raise its P1200 and P2000 to the values about 30 and 40 μmol CO2 m–2 s –1 , respectively, at both 25 and 30o C. At the same T and PPFD, leaves with higher Chl always had higher Pn and stomatal conductance (gs). Yet, the determination coefficient of Pn–gs relationship always higher than that of Pn–Chl, and the slopes of Pn–gs relation were closely related to T. Thus, a significant positive linear regression (Pn = 1.147 + 4.222•gs•T) could be fitted by combining the data measured at different elevation, season and PPFD. The Pn estimated from this equation was closely related to the measured Pn (regression line approximate to 1:1 line, r 2 =0.937, P<0.001). For verifying this equation furthermore, the gs data of the pot-grown M. floridulus at 250 m a.s.l. (from Wong et al., 2014) were conducted to compute the estimated Pn and the results still showed that the estimated value could still correlate to the measured strongly (r2=0.856, P<0.001). Due to gs and T could be determined rapidly and easily by small portable instruments in the field, we concluded this empirical regression model could simulate both the seasonal and diurnal variations of Pn forMiscanthus leaves at different elevations. 本研究於不同季節之高海拔（供試之物種為：高山芒，M. transmorrisonensis，自然分布環境約海拔3000公尺；臺灣芒，M. sinenesis var. formosanus，分布約2,100公尺）及低海拔（五節芒，M. floridurus，海拔約70公尺）地點測量不同葉綠素含量（Chl）之芒草葉片淨光合作用速率（Pn）。冬季高海拔山區氣溫（T）下降至攝氏6度時，高山芒葉片（葉綠素含量介於0.17–0.46gm–2）於測定光照強度1,200μmolm–2s–1下測得之Pn值（P1200）仍可維持0.4–3.2μmol CO2m–2s–1。夏季氣溫回升，於攝氏19度下測量其P1200值可達到3.9–19.9μmol CO2m–2s–1。低海拔地區之五節芒，於攝氏25或30度之氣溫條件下之P1200及P2000（於光照強度2000μmol m–2s–1測得之Pn值）各可高達30及40μmol CO2m–2s–1。於相同測定溫度及光照強度之條件下，葉綠素含量較高之葉片會有較高的Pn及氣孔導度值（gs）。然而，Pn–gs之決定係數（r2）值較Pn–Chl之值高，且Pn–gs之斜率變化與溫度有密切相關。當結合不同海拔、季節、光照強度下測量之資料後可得到顯著正相關之迴歸方程式（Pn=1.147+4.222•gs‧T），其推估之Pn值與實測之Pn值呈高度相關（回歸線為幾近於1：1之直線，r2=0.937,P<0.001）。更進一步以生育於海拔約250m五節芒gs之實測值（數據來自Wongetal.,2014）驗證前揭迴歸方程式，推估之Pn值仍與實測值呈高度相關（r2=0.856,P<0.001）。鑑於現場之gs與T值可藉由可攜式小型儀器快速測得，本研究之芒草屬物種葉片可運用回歸方程式之模型模擬其於不同海拔高度下Pn值之季節及日變化。