光質與光週期對植物工廠內‘美和’菠菜生育之影響

Abstract

菠菜含有豐富的光合色素 (葉綠素、葉黃素與類胡蘿蔔素)、草酸鹽與硝酸鹽，光合色素為對人體有益的成分，濃度越高越好；草酸鹽易與鈣結合在體內形成草酸鈣 (結石症狀)，硝酸鹽在體內形成亞硝酸鹽也有諸多對人體不利的缺點，硝酸鹽在歐盟有規範的上限，草酸鹽則無類似的上限標準可做參考。本研究旨在建立於完全人工光型植物工廠內栽培‘美和’菠菜的人工光源之操作程序，透過對光質與光量的調控，期能栽培出最大產能與最高品質的菠菜。透過針對鮮重與各光合色素電力產能 (Energy Yield, EY) 與光子產能 (Photon Yield, PY) 等指標的計算，來量化評估各栽培條件的優劣。試驗分五方面進行，一、探討不同光質的三種市售 LED 燈管對菠菜生長的影響；二、探討混光 (冷白加上藍光，冷白加上遠紅光) 對菠菜生長的影響；三、由耗能與栽培效率上比較增加兩支遠紅光燈管與增加兩支冷白燈管的差異；四、透過使用遠紅光來延長光照時數並抑制開花的探討及其對菠菜鮮重與光合色素含量累積的影響；五、探討抑制菠菜開花所需的最低遠紅光光照時數與遠紅光光照時機。 結果顯示冷白光加上藍光的處理雖可增加光合色素濃度，但也抑制菠菜生長，降低了單株鮮重與單位面積的光合色素含量。未補充遠紅光的處理組的給光時數上限在 11 小時，在 12 小時的光照下就會有花苞出現，但只需在緊接著 12 小時的明期結束之後補充 2 小時的遠紅光即可抑制開花，在 12 小時的明期之前、中、後段時間內同步照射 2 小時的遠紅光，也可抑制開花。在不使菠菜開花的前提下，使用冷白光照射 14 小時且在明期末期同步提供 4 小時遠紅光照射的處理組可得最大的鮮重 (152.4 g plt-1)，單位面積之葉綠素、葉黃素與類胡蘿蔔素含量可分別達 2406.16、993.53 與 1058.28 mg m-2，EY 與 PYBAR 值分別為 57.33 g kWh-1 與 12 g mol-1 與使用冷白光照射 11 小時處理組的鮮重 (88.96 g plt-1) 相比，年產能提升 71 %，三種光合色素單位面積之含量可分別提升 44 %, 51 % 與 37 %，EY 與 PYBAR 值分別提升了 25 與 23 %。針對單一或多重栽培目標建議選擇的給光方式統整為一個表格，栽培目標包括針對鮮重與/或三種光合色素含量之最大化與/或草酸鹽與/或硝酸鹽含量之最小化，此表格針對消費者對產品的多元需求，應可提供產業界參考。

Spinach has high concentration of photosynthetic pigments (chlorophyll, lutein and carotenoid), oxalate and nitrate, photosynthetic pigments is good for human health, however, oxalate and nitrate should not have excessive intake also for the sake of health. EU had set upper limit of nitrate level in leafy greens but no such standard was set for oxalate. The goal of this study is to investigate on the usage of artificial light to grow spinach ‘Mei Ho’ in plant factory. Various commercially available LED tubes with different spectra were tested. Using quantitative indexes such as EY (energy yield) and PY (Photon yield) of shoot fresh weight and/or contents of photosynthetic pigments, the performance of various cultural procedures can be compared, and the one with the highest outcome and quality can be identified. Totally five experiments were conducted. They are: 1. Investigate on the difference among three commercially available LED tubes on the production of spinach. 2. Investigate on the difference of the mixed light spectra including white plus blue and white plus far-red on the production of spinach. 3. Compare the difference of adding two far-red LED tubes and two cool-white LED tubes on the production of spinach. 4. Different durations of far-red light are tested to inhibite bolting of spinach while light period is longer than critical hour of spinach, which is 12 hours. 5. Investigate on the timing to apply far-red light for the shortest duration derived from previous experiment to inhibite bolting of spinach. . Results showed that cool white mixed with blue light will enhance concentration of photosynthetic pigments, however, it also inhibite the growth, thus leading to the decrease of fresh weight and photosynthetic pigments per production area. With cool white LED tubes only, 11 hour is the critical light period, 12 hours of light will lead to bolting of spinach. Two hours of far-red light right after the photo period of cool-white illumination, the bolting will not happened. Two hours of far-red is provided during the photo period, no matter it is at the first, central or last two hours during the photo period, the bolting can be inhibit. Using cool white LED tubes illuminated for 14 hours with far-red simultaneously at the last 4 hours during the light perod, the bolting can be inhibite and the fresh weight can reach 152.4 grams per plant, the chlorophyll, lutein and carotenoid pigment content can achieve 2406.16, 993.53 and 1058.28 miligram per square meter respectively. Compare with the treatment without using any far-red, the fresh weight only reach 88.96 gram per plant using cool-white LED tubes illuminated for 11 hours per day. The annual production, energy yield (EY) and photon yield (PYBAR) can be enhanceticd by 71, 25 and 23 %, respectively with the help of far-red LEDs. Concentration of three photosynthetic pigments per unit production area can be increased by 44 %, 51 % and 37 %, respectively. The best light treatment subjects to single or multiple targets are compiled. The targets are to derive highest fresh weight, concentration of photosynthetic pigments and/or the lowest concentration of oxalate and/or nitrate. Such Table with targets matching consumers’ need, should be able to serve as a useful tool to the plant factory industry.