環境因子對洋桔梗葉片頂燒與光合作用之影響

Effects of Environmental Factors on Leaf Tipburn and Photosynthesis in Eustoma

王信文(Hsin-Wen Wang)

指導教授 ： 葉德銘

國立臺灣大學/生物資源暨農學院/園藝暨景觀學系/碩士(2015年)

https://doi.org/10.6342/NTU.2015.01996

摘要

洋桔梗[Eustoma grandiflorum (Raf.) Shinn.]葉片頂燒(leaf tipburn)為缺鈣之生理障礙。展開中葉片之蒸散速率低與鈣分布不均為頂燒發生之重要原因，而花芽分化時亦將與展開中葉片競爭鈣而導致葉片頂燒。故本研究以洋桔梗‘國王淡紫’ (‘King of Orchid’)為材料，調查不同光度、溫度與相對濕度(relative humidity, RH)條件之頂燒發展情形。本研究中量測展開中葉片之蒸散速率與葉脈密度，以及觀察洋桔梗莖頂分生組織發育階段，期能了解洋桔梗頂燒發生之原因。另測定各種光度、溫度、蒸氣壓差(leaf to air vapor pressure deficit, VPD)與二氧化碳濃度下洋桔梗葉片之氣體交換速率，欲解釋不同環境條件下頂燒發生率與嚴重程度之差異。並觀察葉面噴施氯化鈣於減輕頂燒之效果，以供產業應用之參考。
本研究中將具有5對完全展開葉、營養生長之洋桔梗植株，於日夜溫36/23℃下，分成12組處理：先於中等相對濕度 (MRH; 76% RH, 206 μmol·m-2·s-1 PPF)1、3、5、7、9天後移至低相對濕度(LRH; 53% RH, 356 μmol·m-2·s-1 photosynthetic photon flux, PPF)，與先於LRH 1、3、5、7、9天後移至MRH，以及處理期間皆在MRH或是LRH環境。植株於連續MRH處理中出現頂燒，而於連續LRH處理則無頂燒發生。於MRH處理5天時植株出現頂燒症狀，而於LRH處理期間並未發生頂燒，當移至MRH環境時才觀察到頂燒發生。
分別將具有4、6或8對完全展開葉片之植株，以36/23℃、76% RH (0.99 kPa VPD)，植株高度光度為206 μmol·m-2·s-1 PPF處理。當植株具有4或6對完全展開葉，分別於處理第18天和第6.5天出現頂燒症狀；當植株具有8對完全展開葉，於處理第5天發生頂燒。
於90% RH、VPD為0.23至0.37 kPa環境下，將具有5對完全展開葉、營養生長之植株以36/23℃與25/18℃處理，分別於處理後之第10天與第18天，肉眼可見頂燒症狀出現於莖頂下數1至3對展開中葉片，以解剖顯微鏡可見莖頂分生組織已形成花萼與花瓣原體。於90% RH下，以36/23℃處理之頂燒發生率與單葉頂燒嚴重程度皆較23/18℃處理高；然而於74% RH下，不論是36/23℃和25/18℃處理皆無頂燒發生。於36/23℃和25/18℃，觀察到以90% RH處理較74% RH處理之莖頂下數第3對展開中葉片蒸散速率低、葉脈密度低，說明90% RH環境下因為鈣吸收與運輸受阻，因此易在葉緣與葉尖出現缺鈣之症狀。
將具有5對完全展開葉、營養生長之植株於日溫28至35℃、夜溫23℃，株高處光度介於205至444 μmol·m-2·s-1環境。當平均相對濕度由71% RH增加至91% RH、VPD自0.32 kPa增至1.19 kPa，頂燒發生率由50%升至100%，其中又以91% RH處理最早發生頂燒、平均全株嚴重程度最高。頂燒症狀出現至發生率達到高峰之天數約為8至14天，且隨著處理相對濕度提高而減少。
於環控條件下測量洋桔梗葉片氣體交換速率。在25℃時，成熟葉之暗呼吸速率為2.6 μmol·m-2·s-1，光補償點為18.2 μmol·m-2·s-1 PPF，而光量子產量為0.04 μmol CO2/μmol PPF。當成熟葉於400 μL·L-1 CO2下，最大淨光合速率為15至18.5 μmol·m-2·s-1，發生於800 μmol·m-2·s-1PPF，葉溫24℃至28℃，與0.48至1.08 kPa VPD；而CO2飽和點為686 μL·L-1，此時葉片之最大淨光合速率為22.5 μmol·m-2·s-1。在VPD為1.07 ± 0.08 kPa時，於光度0至1000 μmol·m-2·s-1 PPF間，蒸散速率維持在2.18至3.28 mmol·m-2·s-1，可見在VPD固定情況下，光度並不影響蒸散速率。固定VPD為1.2 ± 0.1 kPa，當葉溫由16℃升至30℃，蒸散速率也自3.09降至2.06 mmol·m-2·s-1。然而當VPD隨葉溫增加而自0.51 kPa升至4.06 kPa時，蒸散速率自1.60上升至5.25 mmol·m-2·s-1，顯示洋桔梗葉片之蒸散速率主要受VPD影響。當CO2濃度升至1000 μL·L-1後，葉片氣孔關閉，故蒸散速率降至1.84 mmol·m-2·s-1。
葉面噴施氯化鈣對於減輕洋桔梗葉片頂燒之效果於日夜溫31/23℃、平均77% RH (0.82 kPa VPD)，株高處光度介於221 μmol·m-2·s-1PPF之環境中進行。結果顯示每周噴施二次25 mM氯化鈣溶液可減輕頂燒發生率，而每天噴施25 mM，以及每天噴施與每周噴施二次50或100 mM氯化鈣溶液等處理可完全避免葉片頂燒發生，但於100 mM氯化鈣處理中觀察到葉面出現大面積之白化。

關鍵字

生理障礙 ； 蒸散速率

並列摘要

Abstract
Leaf tipburn of Eustoma grandiflorum (Raf.) Shinn. is a calcium-deficient disorder. The published reports of environmental factors on incidence of tipburn are often inconsistent. Low transpiration rate and unbalanced Ca distribution are reported as the main causes of tipburn on unfolding leaves, while differentiating flower competes with the young leaves for Ca also induce tipburn. Eustoma ‘King of Orchid’ was treated with various irradiance, temperature, and relative humidity (RH) conditions to have a better understanding of leaf tipburn. We measured stomatal density, vein density of unfolding leaves, and developmental stages of shoot tips, to elucidate the main cause of leaf tipburn. Leaf gas exchange under various irradiance, temperature, leaf to air vapor pressure deficit (VPD), and CO2 concentration conditions was measured to elaborate the tipburn incidence and severity. Effects of foliar spray of calcium chloride on tipburn occurrence were also investigated.
Eustoma ‘King of Orchid’ plants with five fully expanded leaf pairs were placed in a growth room at 36/23℃. Twelve treatments were conducted as follows: moderate humidity condition (MRH; 76% RH, 206 μmol·m-2·s-1 PPF) for 1, 3, 5, 7, 9 days then moved to low humidity condition (LRH; 53% RH, 356 μmol·m-2·s-1 photosynthetic photon flux, PPF), and LRH conditions for 1, 3, 5, 7, 9 days then moved to MRH, and continuous MRH or LRH treatments. Plants under continuous MRH exhibited tipburn occurrence, while those under LRH did not. Plants expressed tipburn symptoms after 5 days under MRH conditions. In contrast, plants did not express any tipburn under LRH conditions until they were placed to MRH conditions.
Plants at 4th, 6th, and 8th leaf pairs stages were placed under 76% RH (0.99 kPa VPD) and received 206 μmol·m-2·s-1 PPF. Results showed that plants with four or six leaf pairs onset tipburn 18 to 6.5 days after treatment, while plants with eight fully expanded leaf pairs showed tipburn symptoms 5 days after treatment.
Vegetative plants with five fully expanded leaf pairs were placed in growth rooms at 36/23℃ or 25/18℃, and each with 74% RH (0.73 - 1.11 kPa VPD) and 90% RH (0.23 - 0.37 kPa VPD) treatments under 167 to 422 μmol·m-2·s-1 PPF. Results showed that leaf tipburn occurred only in plants at sepal and petal primordia formation under 90% RH conditions, and symptoms appeared 8 days earlier under 36/23℃ than 25/18℃. Plants had a higher incidence and whole-plant severity level were observed at 36/23℃ than at 25/18℃. Consistently lower transpiration and reduced leaf vein density was measured in the third young leaf pairs in plants under 90% RH that may limit the uptake and transport of calcium to the leaf tips.
Vegetative plants with five fully expanded leaf pairs were grown under 28 - 35℃/23℃, and 167 to 422 μmol·m-2·s-1 PPF conditions with six treatments. When humidity was elevated from 71% RH (0.32 kPa VPD) to 91% RH (1.19 kPa VPD), tipburn incidence increased from 50% to 100%. Plants with 91% RH showed the earliest and the most severe tipburn symptoms. It took 8 days for plants with 91% RH and 14 days for those with 71% RH from onset to peak of tipburn incidence.
Characteristics of gas exchange were measured under controlled environments. At 25℃, the dark respiration of mature leaves was 2.6 μmol·m-2·s-1, light compensation point was 18.2 μmol·m-2·s-1 PPF, and quantum yield was calculated as 0.04 μmol CO2/μmol PPF. Maximum net photosynthesis rate (Pn) was 15 to 18.5 μmol·m-2·s-1 at 800 μmol·m-2·s-1 PPF, leaf temperature (TL) between 24 and 28℃, and VPD below 1.08 kPa. CO2 saturation point was estimated as 686 μL·L-1, with maximum Pn was recorded as 22.5 μmol·m-2·s-1. At 1.07 ± 0.08 kPa VPD with irradiance increasing from 0 to 1000 μmol·m-2·s-1 PPF, transpiration rate (E) remained constant at 2.18 to 3.28 mmol·m-2·s-1, indicating that E was not affected by different irradiances when VPD was constant. At 1.2 ± 0.1 kPa VPD, E decreased from 3.09 to 2.06 mmol·m-2·s-1 with increasing TL from 16℃ to 30℃.However, E increased linearly from 1.60 to 5.25 mmol·m-2·s-1 with increasing TL and VPD from 0.51 kPa to 4.06 kPa, indicating that VPD might play a major role in Eustoma transpiration. Exposure to CO2 concentration up to 1000 μL·L-1 reduced stomatal conductance and thus decreased transpiration to 1.84 mmol·m-2·s-1.
Effects of calcium chloride on mitigation of tipburn was studied in plants under 31/23℃ with 77% RH (0.82 kPa VPD) and received 221 μmol·m-2·s-1 PPF. Results showed that spraying 25 mM calcium chloride twice per week reduced the incidence of tipburn, while spraying 25 mM daily, and spraying 50 mM and 100mM daily or twice a week calcium chloride could fully prevent tipburn occurrence. However, leaf bleaching was observed in 100 mM treatments.

並列關鍵字

physiologicl disorder ； transpiration rate

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