薄層屋頂綠化植物選擇與應用之研究

Abstract

薄層屋頂綠化(Extensive green roof)具低承載需求、費用成本低及方便維護管理等特性，但屋頂環境嚴苛且介質層淺薄，故選擇和應用適合的屋頂綠化植物為重要之環節。本研究擬挑選適應臺灣氣候的屋頂綠化植物種類，並提升應用性相關技術為研究重點。植物材料選擇方面，藉由調查臺北地區屋頂綠化施作地點，尋求各季節適用的植物種類，並探討夏季高溫環境下適用之植物及其篩選方式。技術層面上，於臺灣北部不同季節氣候環境，調查適合之維護管理與出貨前馴化措施，最後探討不同育苗容器型式對屋頂綠化植物生長之影響。 臺北地區屋頂綠化植物應用現況方面，垂盆草(Sedum sarmentosum)、怡心草(Tripogandra cordifolia)、麒麟花(Euphorbia milii)及芳香萬壽菊(Tagetes lemmonii)等在不同季節下皆生長良好。而松葉景天(Sedum mexicanum)於春季開花後生長衰弱、小花馬齒牡丹(Portulaca oleracea)和小松葉牡丹(Portulaca gilliesii)低溫下生長較差，藍星花(Evolvulus nuttallianus)因當地環境雨量豐沛造成部分葉片腐爛，台北草(Zoysia matrella)則因後續維護管理不當導致植株枯萎；此外苗期品質亦影響定植後之表現，如黃金萬年草(Sedum acre)。整體而言，影響屋頂綠化植物生長主要因素為植物特性、環境氣候、維護管理及苗期品質。 夏季高溫環境適用植物篩選方面，於夏季期間實際種植28種常見之屋頂綠化植物，生長表現良好者為垂盆草、小松葉牡丹、怡心草、射干(Belamcanda chinensis)、黃邊短葉虎尾蘭(Sansevieria trifasciata ‘Golden Hahnii’)等；而藉由模擬高溫環境篩選耐熱性較佳者為小松葉牡丹、大花松葉牡丹(Portulaca grandiflora ‘Jewel’)、怡心草、小蚌蘭(Rhoeo spathacea ‘Compacta’)和黃邊短葉虎尾蘭。篩選指標中多肉植物以相對葉片厚度與景觀效果相關性較高；而地被植物與景觀效果相關性較高者則為相對葉綠素螢光，故建議不同植物特性可採用不同指標進行評估較為適當。溫度影響多肉植物株型與開花之表現，圓葉景天(Sedum makinoi)適合生長之溫度範圍較廣，萬年草(Sedum hispanicum )具耐寒性，於15/13℃下節間短、植株低矮且葉色轉紅較具觀賞價值；大花松葉牡丹和小花馬齒牡丹則耐熱性佳，於35/30℃外觀表現良好，且開花量多。 維護管理方面，於臺灣北部不同季節下探討灌溉頻度對屋頂綠化植物生長之影響，針對綠薄荷(Mentha spicata)、紅毛莧(Acalypha pendula)、繁星花(Pentas lanceolata)、麒麟花、圓葉景天和斑葉佛甲草(Sedum lineare ‘Variegatum’)，以三種灌溉頻度：未灌溉(NI)、低頻度灌溉(LFI)及高頻度灌溉(HFI)進行試驗。結果顯示春季期間，繁星花、薄荷、紅毛莧灌溉處理六週後其常態化差異植生指數(NDVI)、光化學效率(Fv’/Fm’)和景觀效果較NI處理高，但灌溉處理間無顯著差異；而麒麟花、圓葉景天和斑葉佛甲草表現不受灌溉頻度影響；冬季試驗中所有植物景觀效果均維持7.0分以上，各處理間均無顯著差異；夏季則隨灌溉頻度增加，植物生長越佳。 出貨前馴化措施方面，屋頂綠化植物經馴化作業後有利於定植後之表現，以綠薄荷、麒麟花、越橘葉蔓榕(Ficus vaccinioides)、怡心草於各季節進行增加澆水頻度組(Increase watering, IW)、降低澆水頻度組(Reduce watering, RW)、持續施肥組(Fertilize, F)和噴施抗逆劑(200 μM SA)組之馴化作業。秋季出貨馴化試驗中，綠薄荷、越橘葉蔓榕、怡心草定植後因連日下雨，以IW馴化處理之葉綠素螢光值(Fv/Fm)和景觀效果較高，RW最差。麒麟花則以IW和F馴化處理景觀效果較佳。於定植後F馴化處理初期下降，但後期雨量增加，處理間無顯著差異。於春季期間定植前，綠薄荷和越橘葉蔓榕經噴施200 μM SA和RW馴化處理，定植四週後Fv/Fm和景觀效果表現較佳。麒麟花和怡心草則以F馴化處理生理和外觀表現皆較佳，尤以怡心草較為顯著。同樣於夏季定植前，綠薄荷和越橘葉蔓榕經噴施200 μM SA和RW馴化處理後生長較佳，怡心草則以定植前持續施肥組馴化處理生理和外觀表現皆較佳。 育苗容器型式影響方面，以綠薄荷、繁星花、怡心草、越橘葉蔓榕、麒麟花、圓葉景天和斑葉佛甲草進行不同育苗容器型式試驗，處理分為三寸盆(9 cm pot)、植栽槽(Planting container)和育苗盤(植栽毯, Vegetation mat)。使用植栽槽提前育苗可顯著提高薄荷的存活率和繁星花Fv/Fm表現較佳；越橘葉蔓榕以植栽毯或三寸盆定植，植株皆能生長良好；怡心草則以三寸盆處理為佳；圓葉景天和斑葉佛甲草以植栽毯方式種植較佳，而麒麟花則不受育苗容器型式影響其生長。 綜合上述研究，於臺灣北部從事薄層綠屋頂綠化時，應選擇耐熱、耐旱性強之植物種類，以達到低維護管理之目的；利用相對葉片厚度、相對葉綠素螢光能快速篩選高溫逆境下耐熱性佳之植物。維護管理方面，冬季氣候環境下可不需灌溉、春秋季則建議每週灌溉一次即可；夏季建議可每週灌溉兩次以上，以維持植株之良好生長。出貨前馴化技術可依照不同季節做調整，如多雨季節可於出貨前增加澆水頻度馴化；而高溫乾旱環境則可於定植前四小時噴施200 μM SA或降低澆水頻度馴化處理有助於抵抗屋頂嚴苛環境。育苗方式上，一般植物以植栽槽或植栽毯方式提前育苗較適宜，但生長快速之植物種類，則建議可採用三寸盆移植。總之，除了選擇適合當地氣候環境之植物種類外，應配合完整的育苗、馴化和灌溉管理相關技術，方可提升屋頂綠化植物之應用性，促進臺灣屋頂綠化的發展。

Extensive green roof exerts less load on the building, requires less cost, and is easy to maintain. However, due to the thin layer of substrate coupled with the harsh conditions often found at the rooftop environment, the selection of suitable plants is very important for extensive green roof. The aim of this research is to solve the problems encountered during the growth of green roof plants, with emphasis on selection of plants that suit the climate of Taiwan and improvement of cultivation practices. On the selection of suitable plants, actual green roofs in Taipei were surveyed to investigate the plants used at the different seasons. The adaptability of plants in summer heat and screening method for heat tolerance were also investigated. On the aspect of cultivation practices, suitable green roof maintenance and acclimation measures before dispatch for planting were determined for the different seasonal weather conditions in Taipei. The effect of container type for planters on the quality of the planters was also investigated. Based on the survey of actual green roofs in Taipei, Sedum samentosum, Tripogandra cordifolia, Euphorbia milii, and Tagetes lemmonii performed well in all seasons. Sedum mexicanum deteriorated in growth after flowering in spring, while Portulaca oleracea and Portulaca gilliesii grew poorly at low temperatures. The growth of Evolvulus nuttallianus was affected greatly by the environment, whereas Zoysia matrella withered due to improver cultivation management. The quality of planters also influenced subsequent performance of the plants, such as shown by Sedum acre. Collectively, the main factors that influence the growth of green roof plants were plant characteristics, environmental condition, cultivation management and quality of planters. During summer 28 commonly used green roof plants were grown experimentally on a green roof. Sedum sarmentosum, Portulaca gilliesii, Tripogandra cordifolia, Belamcanda chinensis, and Sansevieria trifasciata ‘Golden Hahnii’ performed well. Portulaca gilliesii, Portulaca grandiflora ‘Jewel’, Tripogandra cordifolia, Rhoeo spathacea ‘Compacta’, and Sansevieria trifasciata ‘Golden Hahnii’ showed good heat tolerance under screening at simulated high temperature environment. Among the selection criteria, relative coverage, relative leaf thickness, and relative chlorophyll fluorescence were closely related to ornamental value. However, a comprehensive evaluation is suggested due to differences in plant characteristics. Temperature affected the appearance and flowering of succulent plants. Sedum makinoi grew under a wide temperature range while Sedum hispanicum showed tolerance to chilling, with short internodes and low growth under 15/13℃, coupled with red coloration of the leaves which increased its ornamental value. Portulaca grandiflora and Portulaca oleracea showed good tolerance to heat, with good growth and highest flower number observed at 35/30℃. On the aspect of maintenance, the effect of irrigation frequency during the different seasons in northern Taiwan on the growth of green roof plants was investigated. Mentha spicata, Acalypha pendula, Pentas lanceolata, Euphorbia milii, Sedum makinoi, and Sedum lineare ‘Variegatum’ were subjected to three irrigation frequencies: no irrigation (NI), low frequency irrigation (LFI) and high frequency irrigation (HFI). The results show that in spring, Pentas lanceolata, Mentha spicata, and Acalypha pendula had higher NDVI and Fv’/Fm’ values and better ornamental value after 6 weeks of irrigation treatment compared with NI treatment, but there was no significant difference between irrigation treatments. Euphorbia milii, Sedum makinoi, and Sedum lineare ‘Variegatum’ were unaffected by irrigation frequency. During winter all plants maintained ornamental value scores of 7.0 and higher and there was no significant difference among treatments. In summer, plant growth improved as irrigation frequency increased. Acclimation procedure before dispatch for planting was found to improve the performance of green roof plants after planting. Mentha spicata, Euphorbia milii, Ficus vaccinioides, and Tripogandra cordifolia were given acclimation treatments of increase watering (IW), reduce watering (RW), fertilize (F), and 200 μM salicylic acid (SA) spray. When the experiment was done in autumn, it rained for days on end after planting. Mentha spicata, Ficus vaccinioides, and Tripogandra cordifolia had higher Fv/Fm and better ornamental value when acclimated with IW, but performed worst when acclimated with RW. Euphorbia milii had the best ornamental value when acclimated with IW or F. The performance of plants acclimated with F decreased at the early stages after planting, but as rainfall increased toward the later stages, there was no significant difference among treatments. In spring, Mentha spicata and Ficus vaccinioides acclimated with RW or sprayed with 200 μM SA had better Fv/Fm and ornamental value 4 weeks after planting. Euphorbia milii and Tripogandra cordifolia acclimated with F treatment had better physiological and ornamental values, and this was especially evident for Euphorbia milii. Similarly, in summer, Mentha spicata and Ficus vaccinioides acclimated with RW or sprayed with 200 μM SA had better growth, whereas Tripogandra cordifolia had better physiological and ornamental values when continually fertilized during the acclimation period. The quality of planters of green roof plants was related to their subsequent growth after planting. The results show that green roof plants were influenced by the container used for the planters. Planters of Mentha spicata, Pentas lanceolata, Tripogandra cordifolia, Ficus vaccinioides, Euphorbia milii, Sedum makinoi, and Sedum lineare ‘Variegatum’ were grown in different containers: 9 cm pot, planting container, and vegetation mat. Using planting container to start the plants increased the survival rate of Mentha spicata and resulted in better Fv/Fm for Pentas lanceolata. Ficus vaccinioides grew well whether grown in vegetation mat or 9 cm pot. Tripogandra cordifolia performed better in 9 cm pot. Sedum makinoi and Sedum lineare ‘Variegatum’ performed better when grown in vegetation mat, whereas the growth of Euphorbia milii was unaffected by container type. In conclusion, for extensive green roof in northern Taiwan, heat- and drought-tolerant plants should be selected for the purpose of low maintenance. Plants with good tolerance against heat stress can be quickly screened with relative leaf thickness and relative chlorophyll fluorescence. As for maintenance, irrigation may not be needed during winter, while weekly irrigation may be sufficient in spring. In summer, irrigation frequency should be twice weekly or more in order to maintain good plant growth. Acclimation before dispatch for planting can be adjusted according to the season, such as increasing irrigation frequency before dispatch during rainy periods. Spraying with 200 μM SA 4 h before planting or acclimating with reduced irrigation could increase the plants’ tolerance to heat and drought that are often encountered in the harsh rooftop environment. As for starting the planters, early planting in planting container or vegetation mat is preferred, but repotting plants grown in 9 cm pots can be done for fast-growing plants. In addition to choosing plants suitable for the local climate, techniques such as growing and acclimating planters and irrigation management should be incorporated to increase the applicability of green roofs and promote the development of green roofs in Taiwan.