Studies on the Photosynthesis of Koelreuteria henryi, aCommon Road Tree in Taiwan

Abstract

本研究之目的在探討臺灣常見的路樹─台灣欒樹(Koelreuteria henryi)葉片在生長發育過程中與不同季節間的光合作用特性之變化。在25℃與飽和二氧化碳環境下測得之光反應曲線資料顯示，台灣欒樹成熟葉之光合作用釋氧最大潛能約為11μmolO2米-2秒-1，飽和光照與光補償點分別為350與4μmol光量子米-2秒-1，光產值約為0.09。不過，在常溫的大氣環境下測得光反應曲線的資料顯示，最大之二氧化碳同化速率為9μmolCO2米-2秒-l，飽和光照與光補償點分剎約為800和20μmol光量子 米-2秒-1，光產值約為0.05。利用光電比色計分析光合色素含量之結果顯示，葉綠索與類胡蘿蔔素的含量隨著葉齡之增加而增加，直到葉成熟為止，則不再增加而維持固定值；但是葉綠素a/b比值則反之，嫩葉較成熟葉高，隨著葉成熟而下降至一固定值。以單位葉綠素重量計算時，光合作用釋氧速率或二氧化碳同化速率，均是嫩葉高於成熟葉；但是以單位葉面積計算時，則是隨著葉的發育先增而後減。至於臺灣欒樹葉的葉綠素含量，則是夏秋季節顯著高於春冬季節。對於台灣欒樹所具的光合作用特性也有所討論。

The aim of this study was to investigate developmental and seasonal changes in photosynthetic characteristics of leaves of the common road tree in Taiwan, Koelreuteria henryi. The data from the light response curve of oxygen evolution measured at 25°C and saturating CO2 showed that the potential of photosynthesis was 11μmol O2 m-2s-1, the saturating light and the compensation point were about 350 and 4μmol quanta m-2s-1 respectively, and quantum yield was about 0.09 in mature leaves. However, the data from CO2 assimilation determined at ambient air and temperature showed that the maximum rate of photosynthesis was about 9μmol CO2 m-2 s-1, the saturating light and the compensation point were about 800 and 20μmol quanta m-2s-1, respectively, and quantum yield was about 0.05. Spectrophotometric analysis of chlorophyll a, b and carotenoids showed that pigment content increased with development and remained constant after maturation. The chlorophyll a/b ratio decreased after maturation and kept constant there after. On a chlorophyll basis, photosynthetic rates of oxygen evolution and CO2 assimilation were higher in younger leaves than mature leaves, but on a leaf area basis, the rates increased first and then decreased during development. Chlorophyll contents were higher in summer and autumn leaves than spring and winter. The photosynthetic characteristics in leaves of Koelreuteria henryi were discussed.