介質體積含水量對夏秋季花壇植物生長與光合作用之影響

Effects of Volumetric Water Content on Growth and Photosynthesis of Summer-Autumn Flowering Bedding Plants

夏秋季花壇植物應用於戶外景觀綠美化，易遭遇乾旱及淹水逆境。本研究以電容式土壤水分測量儀WET Sensor（Type HH2, Delta-T Devices, Cambridge, UK）測量介質體積含水量（volumetric water contents, VWC），探討VWC對臺灣常見夏秋季花壇植物生長狀況及觀賞品質之影響，並測量光合作用參數，以判斷參試植物之耐旱性及耐濕性。試驗結果顯示所有參試植物皆以40% VWC處理組有最佳生長與品質表現。日日春[Catharanthus roseus（L.）G. Don]六品種中，除‘Mediterranean’外，皆以70% VWC潮溼處理之花朵數、花朵直徑及觀賞品質最低，且葉片出現黃化或落葉現象。20% VWC乾旱處理之植株地上部較小，但仍能維持觀賞品質，顯示參試之日日春五品種皆稍耐旱但不耐濕。而‘Mediterranean’在70% VWC處理仍維持花朵開放及下位葉不脫落，為較耐濕的日日春品種。以20% VWC乾旱處理之‘New Look Red’雞冠花（Celosia cristata L.）與‘BuddyPurple’千日紅（Gomphrena globosa L.）生長與品質尚佳，無明顯逆境表現；而70% VWC處理下淨光合作用速率下降，花序及葉片萎凋，觀賞品質不良，顯示參試之‘New Look Red’雞冠花與‘Buddy Purple’千日紅為稍耐旱但不耐濕之花壇植物。‘Million Gold’黃帝菊[Melampodium paludosum（Pers）DC.]在20%或70% VWC處理之花朵數、分枝數、地上部乾重與Pn值皆較40% VWC處理低，觀賞品質不良，顯示‘Million Gold’黃帝菊不耐長期乾旱或潮濕。‘Green Cloud’彩葉草[Solenostemon scutellarioides（L.）Codd.] 70% VWC處理之生長與觀賞品質俱佳，20% VWC處理之株型較小但可維持觀賞品質，顯示‘Green Cloud’彩葉草為稍耐旱、喜濕之植物。所有參試植物在20/70%乾旱復水處理之生長量雖未如40%VWC處理佳，但株型較緊湊，也可維持開花及良好觀賞品質。 Summer-flowering bedding plants, widely used in urban landscape, are often under drought or waterlogging conditions. In this research, we determined growth and photosynthesis of several popular summer bedding plants under 40% volumetric water content (VWC), 70% VWC (moisture), 20% VWC (drought), and 20/70% (drought/moisture) VWC as measured with a WET sensor. All tested plants grown best under 40% VWC after treatments for 35 days. Five cultivars of Catharanthus roseus (L.) G. Don under 70% VWC treatment had the lowest flower number and flower diameter, and exhibited leaf chlorosis and leaf drop; while those under 20% VWC treatment maintained flowering and deep green color leaf, with good quality. Thus, Catharanthus roseus was categorized as drought-tolerant and moisture-intolerant species. 'Mediterranean Rose Halo' maintained flowering, with less leaf drop, and good plant quality when grown under 70% VWC treatment, suggesting that 'Mediterranean Rose Halo' might be a moisture-tolerant Catharanthus roseus cultivar. Celosia cristata L. ‘New Look Red’ and Gomphrena globosa L. 'Buddy Purple' grown under 70% VWC had wilted inflorescences and leaves and poorest plant quality. The 70% VWC treatment decreased net photosynthesis (Pn) in Celosia mainly through stomatal limitation and in Gomphrena globosa through both stomatal and non-stomatal limitation. Celosia cristata and Gomphrena globosa under 20% VWC treatment did not express any stress symptoms and maintained good growth and quality, and thus they were categorized as drought-tolerant and moisture-intolerant species. Melampodium paludosum (Pers) DC. 'Million Gold' had the fewest flowers and branches, and lowest shoot dry weight and Pn when grown under 20% and 70% VWC treatments, i.e. Melampodium paludosum could not tolerate long-term drought or moisture conditions. Solenostemon scutellarioides (L.) Codd. 'Green Cloud' under 70% VWC remained excellent growth and plant quality, while plants under 20% VWC were smaller but had no obvious stress symptoms. Therefore, Solenostemon scutellarioides was categorized as drought-tolerant and moisture-loving species. All the tested plants under 20/70% VWC were compact and acceptable, although they were smaller than those under 40% VWC treatment.