洋桔梗連作障礙成因及改善之研究

Abstract

洋桔梗為原生於美國內布拉斯加州和科羅拉多州南部至北墨西哥之草本花卉，因其花形與花色多樣化瓶插壽命長，深受消費者喜愛。在日本相當受到歡迎，但當地冬季生產洋桔梗切花，需於設施內加溫，生產成本極高。而臺灣冬季氣候適合洋桔梗生長，每年11月至隔年4月生產切花外銷日本。而近年臺灣設施內洋桔梗出現連作障礙，嚴重影響栽培與生產，迄待解決。本研究探討土壤植體殘留、土壤及養液EC值與有機酸對洋桔梗生長與開花之影響，及土壤淋洗與添加活性碳處理期能改善洋桔梗之連作障礙。 取雲林虎尾之洋桔梗連作土，分析結果顯示土壤為砂粘壤土，粘粒比例高(20%)，土壤孔隙度28.6%與田間容水量17.7%皆偏低，不利根系發育。有機質含量為5.14%，酸鹼值與電導度值分別為7.9 (1：2，w/v)與1.54 dS·m-1 (1：5，w/v)，土壤有效性磷、鉀、鈣、鎂濃度皆高於推薦值3倍以上，顯示鹽分累積。於秋季以連作土壤種植288格穴盤苗之洋桔梗28天後，參試之品種皆較未種植過洋桔梗之田土處理組矮且展幅小、根尖細胞丙二醛含量增加。植體分析顯示並無元素缺乏；但剛完全展開葉片之光系統II參數最大光子利用效率(Fv/Fm)與光化學焠熄係數qP值下降。 為了解根泌有機酸與高濃度養液對洋桔梗生長之影響，以200% (EC值3.76 dS·m-1)之強生氏養液水耕栽培洋桔梗ʻCroma Ш Whiteʼ，養液內分別添加不同濃度(0、0.4、0.8、1.2、1.6、2.0、2.4、2.8 mM)順丁烯二酸、苯甲酸、蘋果酸與間羥基苯甲酸等有機酸，結果顯示200%強生氏養液內含有前述有機酸，皆會抑制洋桔梗生長，包含株高下降、節數、節間長度與莖徑減少、全株葉面積降低、地上部乾重累積減少，且隨添加濃度提高，抑制生長情形加劇。另以200%強生氏養液水耕分別添加1.6 mM前述4種有機酸，將不同發育階段之洋桔梗苗種植35天，結果顯示洋桔梗4週與5週苗齡者對於高EC值養液環境加上有機酸處理之耐受性較低，苯甲酸或間羥基苯甲酸處理更明顯。再將前述4種有機酸等量混加於200%強生氏水耕養液內種植洋桔梗，濃度超過1.6 mM時，植株生長量、光合作用速率與可見花苞之比率皆下降，植體分析地上部氮、磷與鈣等濃度下降，鎂與鐵濃度上升，植株多簇生化。綜合連作土壤理化分析及有機酸與高濃度養液添加之結果，高EC值土壤與養液條件下，配合植體殘留或添加有機酸，會造成洋桔梗生長與花苞發育延遲，甚至花苞未出現。 以不同溫度(25℃、50℃、100℃)與不同水量(100、200、300 mL)澆灌盆植(盆底直徑8.9 cm，體積600 mL)連作土壤，結果顯示以100℃ RO (reverse osmosis, RO)水單盆澆灌300 mL淋洗土壤後，洋桔梗ʻArena Pinkʼ株高、節數、節間長、全株葉面積與地上地下部乾重等生長數值恢復，根尖細胞丙二醛含量降低，光合作用速率與電子傳遞鏈能力明顯上升。另連作土壤拌入不同比例活性碳搭配水溫水量澆灌處理，以改善洋桔梗連作障礙，結果顯示連作土壤拌入0.05%-0.1% (v/v)活性碳，雖可改善洋桔梗ʻArena Pinkʼ株高、節數、節間長、全株葉面積與地上地下部乾重等生長勢不佳問題，但不同年度試驗結果顯示，活性碳拌入比例超過0.1% (v/v)效果不穩定。連作土壤添加活性碳搭配不同溫度澆灌處理並無加乘效果。另以小分子有機酸定量分析結果顯示，100℃土壤淋洗液中含有苯甲酸，顯示其與連作障礙有關。

Eustoma grandiflorum, commonly known as lisianthus, is a herbaceous flowering plant native to Nebraska and southern Colorado in the United States, extending to northern Mexico. It is highly favored by consumers due to its diverse flower shapes and colors, as well as its long vase life. In Japan, Eustoma is particularly popular; however, the production of cut flowers during the wintertime necessitates the use of heated facilities, which significantly increases production costs. In contrast, winter climate of Taiwan is suited for Eustoma cultivation, with cut flowers produced from November to April for export to Japan. Nevertheless, in recent years, greenhouse in Taiwan have faced continuous cropping issues with Eustoma, which have severely impacted cultivation and production. These challenges remain unresolved. This study examined the effects of soil with plant residues, soil or nutrient solution electrical conductivity (EC), and organic acids on the growth and flowering of Eustoma. Additionally, it explored whether soil leaching and the addition of activated charcoal could mitigate the contiuous cropping problems. The continuously cropped soil (CCS) from the Huwei area of Yunlin was analyzed, and the results indicated that the soil is sandy clay loam with a high proportion of clay. The organic matter content was 5.14%, with a pH value of 7.9 (1:2, w/v) and an electrical conductivity value of 1.54 dS·m⁻¹ (1:5, w/v). The soil had high levels of available phosphorus, potassium, calcium, and magnesium. After planting Eustoma seedlings in 288-cell trays using the CCS for 28 days in the autumn, the cultivars exhibited growth reduction and smaller plant width compared to the control, which had not been planted with Eustoma. Additionally, root malondialdehyde content increased. Plant tissue analysis revealed no deficiencies in essential elements. Moreover, the photosystem II maximum photon use efficiency (Fv/Fm) and the photochemical quenching coefficient (qP) decreased in recently fully expanded leaves. In order to realize the effects between root-secreted organic acids and high concentration nutrition solution, in a hydroponic cultivation of Eustoma ‘Croma III Whiteʼ using 200% Johonson’s solution (EC value 3.76 dS·m⁻¹), different concentrations (0, 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, and 2.8 mM) of maleic acid, benzoic acid, malic acid, and p-hydroxybenzoic acid were added to the nutrient solution. Results showed that the presence of these organic acids in the 200% Johonson’s solution inhibited Eustoma growth, including reduction in plant height, node number, internode length, and stem diameter, as well as decrease in leaf area and retardation in shoot dry weight accumulation. Furthermore, the inhibitory effects on growth aggravated as the concentration of the organic acids increased. In a hydroponic cultivation of Eustoma using 200% Johonson’s solution, 1.6 mM of the four organic acids were added at various seedling developmental stages and cultivated for 35 days. Results showed that the seedlings of 4-week and 5-week ages had lower tolerance to high EC solution environment when treated with organic acids, with the inhibitory effects being more pronounced with benzoic acid or p-hydroxybenzoic acid. When the four organic acids were mixed in equal amounts and added to the 200% Johonson’s solution, the plant growth, photosynthesis rate, and the visible flower bud formation rate decreased when the concentration exceeded 1.6 mM. Plant tissue analysis revealed a decrease in the concentrations of nitrogen, phosphorus, and calcium in the shoots, while magnesium and iron concentrations increased. And many plants were in a rosette growth pattern. Pre-planting irrigation treatments were conducted using potted CCS (8.9 cm-diameter pot, 600 mL), and irrigated with reverse osmosis (RO) water at various temperatures (25°C, 50°C, 100°C) and volumes (100, 200, 300 mL). The results showed that when 300 mL of 100°C RO water was used to leach the soil in a single pot, the plant growth of Eustoma ‘Arena Pink’ was recovered. Additionally, root malondialdehyde content decreased, while the photosynthetic rate and electron transport chain rate significantly increased. CCS was mixed with various proportion of activated charcoal (AC) and irrigated with different water temperatures and volumes. Results showed that adding 0.05% - 0.1% (v/v) AC into the continuously copped soil improved growth, but the effectiveness was inconclusive. Moreover, no synergistic effects were observed when AC was combined with different irrigation temperatures. Additionally, quantitative analysis of small molecule organic acids revealed that the leachate from CCS treated at 100°C contained benzoic acid, suggesting that the presence of benzoic acid in the CCS was related to the continuous cropping issues.