葉片顏色與人為遮陰對兔眼藍莓葉片氣體交換及植株生長之生理影響

Abstract

國內新鮮藍莓的進口量持續增加，又面對農業人口老化，栽培管理輕簡且單價高的藍莓在臺灣具有發展潛力。於臺北平地栽培之兔眼藍莓(Vaccinium ashei Reade)開花結實良好，但夏季午間嫩稍常現暫時性萎凋，因此夏季高溫高光之逆境可能不利植株生長。本論文首先探討葉片色澤是否可作為兔眼藍莓耐熱性之指標；另進行人為遮陰試驗，預期在滿足光合作用光飽合點下，避免植株負荷過量之太陽能，能增進其光合作用能力及營養生長。 試驗一自兔眼藍莓‘Blueshower’開放授粉的後代中，選取葉片色澤亮度不同之植株，測量其葉片溫度(TL)及氣體交換。葉面色澤較深之植株，葉溫與氣溫差值(∆T)在正午前較葉色淺者高，午後則趨於相近。在不同基因型植株間，葉面亮度與葉片氣孔導度(gs)或淨光合作用速率(An)無關，各植株皆於葉溫約35°C測得最高An值。葉面色澤較深之植株，正午之蒸散速率(E)較高，以至於水分利用效率(WUE)較低。 試驗二於夏季高溫期間以輕度(20%)或中度(35%)遮光率之白色針織網，對三年生之盆植兔眼藍莓進行遮陰處理，並以未遮陰者為對照，測量葉片之氣體交換、葉綠素含量、葉綠素螢光，並調查植株營養生長量及隔年果實產量。高溫晴朗的天候下，樹冠外層成熟葉片之PSⅡ最大光能轉換效率(Fv/Fm)及PSII實際光能轉換效率(ΦPSII)下降，遮陰下兔眼藍莓‘Blueshower’正午之Fv/Fm及ΦPSII較高，但未遮陰者亦僅輕微下降，顯示葉片生理活性在高溫高光下未受嚴重光抑制。35%遮陰下‘Tifblue’之葉片溫度(TL)及葉片與大氣蒸氣壓差(VPDL-air)降低，gs及An較未遮陰者高約30%，但E則未受顯著影響，因而WUE較高。遮陰對兔眼藍莓植株生理的正面影響，僅在氣溫高於35.5°C且光照充足下較顯著，以至於在臺北夏季雖高溫但頻繁多雲的天候下，遮陰的效益不足以改變兔眼藍莓植株生長量及隔年果實產量。

The rabbiteye blueberry (Vaccinium ashei.) is a promising new fruit crop in Taiwan’s subtropical lowland. However, mid-day temporarily wilting of young shoot tips often occurs in the high summer heat and irradiance. This thesis investigated that 1) how leaf color of diffent genotypes responses to heat and light stress and 2) can artificial shading avoid overload of solar energy but maintain light above the saturation point of leaf photosynthesis to improve photosynthesis and vegetative growth in rabbiteye blueberry. Leaf temperature (TL) and gas exchange of ‘Blueshower’ open-pollinated seedlings with leaves of different shades of green were monitored. Leaf-air temperature differences (∆T) in genotypes with dark green leaves were greater than those with light green leaves before solar noon but were undistinguishable among genotypes after solar noon. There was no special correlation between leaf lightness and leaf stomatal conductance (gs) or net assimilation rate (An). Maximum An was recorded at leaf temperature around 35˚C in all genotypes. Mid-day transpiration rates (E) in genotypes with dark green leaves were higher than those with light green leaves. Consequently, water use efficiency (WUE) in genotypes with dark green leaves was lower than that with light green leaves. Container grown 3-year-old rabbiteye blueberries were lightly (20%) or moderately (35%) shaded with white knitted shade cloth and compared with the unshaded control during the summer heat. Leaf gas exchange, chlorophyll content, chlorophyll fluorescence, vegetative growth, and fruit yield of the following year were measured. On hot sunny days, the dark-adapted photosystem II efficiency (Fv/Fm) and quantum efficiency of photosystem II electron transport (ΦPSII) of mature exposed leaves decreased. The decreases in Fv/Fm and ΦPSII in midday were slightly smaller for ‘Blueshower’ plants under shading but were not statistically differed from the unshaded control, indicating no severe photoinhibition. The lower TL and smaller leaf-to-air vapor pressure deficit (VPDL-air) of ‘Tifblue’ under the 35% shading treatment improved leaf An and gs by 30% higher than those of the control. WUE was imporved by shading although E was not affected. the positive physiological effects of shading were only obvious in conditions with high irradiance and air temperature above 35°C. Therefore, the benefits of shading did not reflect on seasonal vegetative growth or yield of rabbiteye blueberries in northern Taiwan with a hot but frequently cloudy weather condition in the summer.