環境因子對文心蘭光合作用之影響

Effects of Environmental Factors on Photosynthesis of Oncidium Alliance

陳筱薇(Hsiao-Wei Chen)

指導教授 ： 張耀乾 ； 李哖

國立臺灣大學/生物資源暨農學院/園藝學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.02311

摘要

許多植物之光合作用速率於午間降低，此現象被稱之為午休現象 (midday depression)。夏季午後，文心蘭光合作用常有降低情況，可能造成植株生長及開花品質較差。夏季中午，高光常伴隨者高溫，因此很難理解何者為促使午休現象之關鍵因子。本研究在找出Oncidium Gower Ramsey於不同環境 (包含有環控及無環控下) 之光合作用特性，以探討導致文心蘭光合作用午休現象之原因。
　　Onc. Gower Ramsey於15-25 °C之生長箱下有較高之淨光合作用速率 (Pn) 約4 μmol•m-2•s-1，光合作用速率在高於26 °C即有明顯下降現象。Onc. Gower Ramsey光飽和點約於250 μmol•m-2•s-1，當光度超過此飽和光度，也會造成光合作用速率下降。然而，當光度在500 μmol•m-2•s-1內，光合作用速率下降較少。CO2濃度於600 μL•L-1時，Onc. Gower Ramsey有最高之淨光合作用速率。
　　Onc. Gower Ramsey光合作用日變化因生長於不同環境而異。晴天於不同環境下，在簡易網室中所測得之淨光合作用速率比於人工氣候室及生長箱測量者為低。高溫對文心蘭光合作用有不利影響，造成光合作用午休現象之發生；而當溫度低於15 °C則可能使午休現象減緩或不發生。將文心蘭置於人工氣候室日/夜溫 25/20 °C及35/30 °C環境下，測量不同溫度及午間移溫處理對光合作用日變化之影響，若將原本於35 °C測量之Onc. Gower Ramsey移置25 °C繼續測量，結果顯示出其光合作用降低情況可明顯回復。Onc. Gower Ramsey對短時間內溫度變化之反應敏感。
　　測量Onc. Gower Ramsey ‘Sunkist’、Onc. Gower Ramsey ‘Volcano Queen’及Colmanaras Wildcat之光合作用日變化曲線，其中淨光合作用速率以Onc. Gower Ramsey ‘Sunkist’最高，且其發生午休現象後之回復力亦較佳。三種文心蘭間之Fv/Fm值 (PSⅡ電子利用速率)，以Onc. Gower Ramsey ‘Sunkist’較高，而Onc. Gower Ramsey ‘Volcano Queen’及Colm. Wildcat較低，三者有明顯差異。葉綠素螢光 (Fv/Fm) 與淨光合作用速率之日變化曲線相似，可相互參考以供判斷植物有無遭受逆境之影響。
　　將文心蘭L2葉片由葉尖到葉基分成四區，以離葉尖較近之二區進行取樣，較不會因取樣部位而造成Pn及Rubisco活性差異。葉溫達30 °C以上時，Pn及Rubisco活性有下降情況發生。隨著光度變化，文心蘭Pn與Rubisco活性變化曲線有相似趨勢。將葉溫、光度、氣孔導度、Rubisco活性及Pn之間進行廻歸分析，結果顯示葉溫為影響文心蘭Pn快速下降之主因，高葉溫亦會導致氣孔導度降低，而光度高低及Rubisco活性在本研究中則與光合作用速率下降的相關性較低。

關鍵字

文心蘭 ； 光合作用 ； 午休現象 ； 蘭花

並列摘要

Photosynthetic rate is often reduced during midday in some crops, this phenomenon has been termed as midday depression (MD). Oncidium also suffers greatly from MD in the summer, resulted in reduced growth and poor flowering quality. Since high radiation usually accompanies high temperature during midday in the summer, it is difficult to figure out the key factor that promotes MD. We thus investigated photosynthetic activities of Onc. Gower Ramsey in a variety of conditions, environment-controlled and non-environment-controlled, and then discussed the reasons that caused photosynthesis reduction at noon in the summer.
　　In a growth chamber, net photosynthesis (Pn) of Onc. Gower Ramsey was about 4 μmol•m-2•s-1 between 15-25 °C, and declined dramatically when temperature was higher than 26 °C. Photosynthesis was also reduced when photosynthetic photon flux density (PPFD) exceeded the saturating point for Onc. Gower Ramsey, which is approximate 250 μmol•m-2•s-1, while the reduction was slight when PPFD was below 500 μmol•m-2•s-1. When CO2 concentration reached 600 μL•L-1, Pn of Onc. Gower Ramsey reached its maximum.
　　When Onc. Gower Ramsey was grown under different environments its daily photosynthetic patterns changed. On sunny days, the average Pn of Oncidium grown outdoor in a rain shelter was lower than that in a phytotron or in a growth chamber. The results revealed that high temperature is the major factor causing photosynthesis rate of Oncidium to decline. Midday depression was eased or totally suppressed when temperature was lower than 15 °C. Changes of Pn before and after reciprocal transfer between 25/20 °C and 35/30 °C growth regimes at 11:00AM showed that Onc. Gower Ramsey is sensitive to short-term temperature changes. When Onc. Gower Ramsey was transferred from 35 °C to 25 °C, its photosynthetic depression was relieved.
　　Among Onc. Gower Ramsey ‘Sunkist’, Onc. Gower Ramsey ‘Volcano Queen’ and Colmanaras Wildcat, Onc. Gower Ramsey ‘Sunkist’ had the maximum Pn and the best recovering ability after midday depression. The Fv/Fm value (an indicator of PSⅡ electron transport efficiency) of Onc. Gower Ramsey ‘Sunkist’ was higher than that of Onc. Gower Ramsey ‘Volcano Queen’ and Colm. Wildcat. The diurnal change curves of chlorophyll fluorescence as measured by Fv/Fm and net photosynthesis were similar. To know whether Oncidium plant is under environmental stress, measurement of chlorophyll fluorescence or Pn curve is an option.
　　Net photosynthesis and Rubisco activity were measured from the regions close to the tip of L2 leaves, subjected to different temperatures. When the temperature was higher than 30 °C, both Pn and Rubisco activity decreased. Also, Pn and Rubisco activity curves exhibited a similar trend associated with the change of light intensity. By regression analysis of Pn changes with leaf temperature, light intensity, stomatal conductance, or Rubisco activity, temperature appeared to be the main parameter causing Pn reduction. In addition, high temperature caused stomatal conductance to decline. The results suggest that light intensity and Rubisco activity are not the major causes for MD in Oncidium Gower Ramsey.

並列關鍵字

Oncidium ； photosynthesis ； midday depression ； orchid

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