Photosynthetic capacity of Miscanthus species at high and low elevations of sub-tropical Taiwan through different seasons and the relationships with chlorophyll content and stomatal conductance

Net photosynthetic rate (P_n) 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℃, the P_n 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 P_(1200)) could retain 0.4-3.2 μmol CO_2 m^(-2) s^(-1). While in the summer, the P_(1200) measured at 19℃ could raise to 3.9-19.9 μmol CO_2 ^(-2) s^(-1). At low elevation, M. floridulus could raise its P_(1200) and P_(2000) to the values about 30 and 40 μmol CO_2 m^(-2) s^(-1), respectively, at both 25 and 30℃. At the same T and PPFD, leaves with higher Chl always had higher P_n and stomatal conductance (g_s). Yet, the determination coefficient of P_n-g_s relationship always higher than that of P_n-Chl, and the slopes of P_n-g_s relation were closely related to T. Thus, a significant positive linear regression (P_n = 1.147 + 4.222．g_s．T) could be fitted by combining the data measured at different elevation, season and PPFD. The P_n estimated from this equation was closely related to the measured P_n (regression line approximate to 1:1 line, r^2=0.937, P＜0.001). For verifying this equation furthermore, the g_s data of the pot-grown M. floridulus at 250 m a.s.l. (from Wong et al., 2014) were conducted to compute the estimated P_n and the results still showed that the estimated value could still correlate to the measured strongly (r^2=0.856, P＜0.001). Due to g_s 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 P_n for Miscanthus leaves at different elevations.

關鍵字

chlorophyll content ； C_4 plants ； Miscanthus ； photosynthesis ； stomatal conductance

並列摘要

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3,000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（P_n）。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0.17-0.46 g m^(-2)）於測定光照強度1,200 μmol m^(-2) s^(-1)下測得之P_n值（P_(1200)）仍可維持0.4-3.2 μmol CO^2 m^(-2) s^(-1)。夏季氣溫回升，於攝氏19度下測量其P_(1200)值可達到3.9-19.9 μmol CO^2 m^(-2) s^(-1)。低海拔地區之五節芒，於攝氏25或30度之氣溫條件下之P_(1200)及P_(2000)（於光照強度2,000μmol m^(-2) s^(-1)測得之P_n值）各可高達30及40 μmol CO^2 m^(-2) s^(-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P_n及氣孔導度值（g_s）。然而，P_n-g_s之決定係數（r^2）值較P_n-Chl之值高，且P_n-g_s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．g_s．T），其推估之P_n值與實測之P_n值呈高度相關（回歸線為幾近於1:1之直線，r^2=0.937, P＜0.001）。更進一步以生育於海拔約250 m五節芒g_s之實測值（數據來自Wong et al., 2014）驗證前揭迴歸方程式，推估之P_n值仍與實測值呈高度相關（r^2=0.856, P＜0.001）。鑑於現場之g_s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P_n值之季節及日變化。

並列關鍵字

葉綠素含量； C4型植物；芒草屬；光合作用；氣孔導度

國際替代計量

Photosynthetic capacity of Miscanthus species at high and low elevations of sub-tropical Taiwan through different seasons and the relationships with chlorophyll content and stomatal conductance

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