本研究利用SPME（solid-phase micro-extraction）技術分析紅檜（Chamaecyparis formosensis）與臺灣扁柏（C. obtusa var. formosana）在水分正常與乾旱逆境下葉子萜類化合物之變化。試驗結果顯示，紅檜遭受逆境後，除oxygenated monoterpenes相對含量由5.64%下降至0.76%之外，其他萜類成分組成無顯著差異；然而，臺灣扁柏葉子在逆境後之monoterpene hydrocarbons相對含量增加近2倍，oxygenated monoterpenes相對含量則由15.22%下降至2.03%。單萜類化合物的oxygenated telpenes與non-oxygenated terpenes彼此間的消長，可能是合成途徑中彼此位於同一階層的競爭關係所致。乾旱逆境時，有些植物酚類化合物的相對含量會增加，且揮發成分中oxygenated terpenes含量較豐富，故具有較高的自由基捕捉能力；因此，本研究中oxygenated terpenes含量的減少，可能為減少植物細胞膜之氧化壓力避免傷害而犧牲；當逆境持續，是否oxygenated terpenes相對含量又將逐漸提高，則有待後續深入的探討。

In this study, SPME (solid-phase micro-extraction) technique was used to analyze the terpenoids in leaves of Chamaecyparis formosensis and C. obtusa var. formosana under normal water conditions and drought stress. The results showed that the relative contents of oxygenated monoterpenes in C. formosensis decreased from 5.64% to 0.76% after drought stress, while the other terpenoids showed no significant difference. On the other hand, the relative contents of monoterpene hydrocarbons in C. obtusa var. formosana increased nearly 2-fold after drought stress, and the relative contents of oxygenated monoterpenes decreased from 15.22% to 2.03%. The fluctuation of oxygenated terpenes and non-oxygenated terpenes of monoterpenoids might be caused by the competition in the same biosynthesis pathway-level. The relative content of phenolic compounds in some plant species increased under drought stress, and the higher content of oxygenated terpenes lead to higher free radical scavenging capacity. Therefore, the reduction of oxygenated terpenes in this study might be a sacrifice to reduce the plant cell membrane damage from oxidative stress. Further exploration will be needed in the future to answer whether the relative content of oxygenated terpenes will gradually increase if drought stress continues.