植物的氣孔 (stomata) 在光合作用及蒸散作用中扮演重要的角色，不僅影響植物生長與適應環境，更與大氣中的碳循環和水循環息息相關。一般認為當環境條件改變時，氣孔會有所反應而改變其孔徑大小。然而，過去對於氣孔的研究較少著重於蕨類植物等較古老的植物類群，因此其氣孔對於環境變化之敏感性仍未有所定論。近年來的研究對蕨類氣孔在環境二氧化碳濃度改變之下的反應情形充滿爭議。為了解蕨類植物的氣孔對於環境二氧化碳濃度變化之敏感性以及其對植物的影響，本研究測量9種蕨類植物、1種石松植物以及2種被子植物的葉片在合適的溫度、濕度及光線下改變環境二氧化碳濃度後的氣孔導度 (stomatal conductance) 變化率、達到氣孔導度變化率之一半時的所需時間、細胞間隙與不同環境二氧化碳濃度的比值 (ci/ca ratio) 以及在高環境二氧化碳濃度下的水分利用效率。結果顯示當環境二氧化碳濃度降低後，各研究物種的氣孔導度皆會明顯地提高，氣孔開啟的速度接近；當環境二氧化碳濃度升高時，氣孔導度都會明顯地降低，水分利用效率也因而顯著提升，大多數物種間的氣孔閉合速度並無明顯差異。不同環境二氧化碳濃度下的ci/ca值無明顯差異。氣孔感應環境二氧化碳濃度變化而改變其孔徑大小的敏感性機制存在於蕨類植物、石松植物及被子植物中，但反應程度可能受到其他因素而有所不同。本研究結果有助釐清蕨類氣孔受到環境二氧化碳濃度變化的敏感性，幫助了解氣孔功能的演化以及其對植物適應環境的影響。

The stomata of plants play an essential role in photosynthesis and evapotranspiration, affecting not only the growth and adaptation of plants, but also the carbon cycle and water cycle. It is generally believed that when environmental conditions change, the stomata will response and alter their pore sizes. However, relatively few studies of stomata have focused less on more ancient groups of plants such as ferns, so the sensitivity of their stomata to environmental changes remains unclear. Recently, the response of fern stomata to changes of ambient CO2 concentration, is controversial. In order to investigate the sensitivity of fern stomata to changes of ambient CO2 concentration and its effects on the plants, the change rate of stomatal conductance of 9 species of ferns, 1 lycophytes, and 2 angiosperms after changing the ambient CO2 concentration were measured under appropriate temperature, humidity and light. The half-time of each step was also recorded. In addition, the ratio of intercellular to ambient CO2 concentration, ci/ca ratio, over each step and water-use efficiency under high ambient CO2 concentration were calculated. The results showed that when the concentration of ambient CO2 reduced, the stomatal conductance of all species significantly elevated, and the half-time of stomatal openness was similar among species; when the concentration of ambient CO2 increased, the stomatal conductance of all species significantly dropped, which enhanced the water-use efficiency. The response half-time of the stomatal closure was not different among most species. The ci/ca ratio among each ambient CO2 was not significantly different. The mechanism that stomata can sense the change of ambient CO¬2 concentration and adjust their pore size exists in ferns, lycophytes, and angiosperms, the but the degree of response may be different due to other factors. The results of this research may help to clarify the sensitivity of fern stomata to the change of ambient CO¬2 concentration, which can help to understand the evolution of stomatal function and its impact on plant adaptation to the environment.

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