Potential of mosses in urban greening under subtropical climate

M.Phil.Urban greening plays a significant role in alleviating environmental problems like urban heat island effect, air pollution and storm water runoff. However, densely populated metropolitans can only provide limited spaces for greening, which calls for new models of urban greening. Recently, mosses have received greater attention as a new type of greening material. This group of inconspicuous tiny plants have their advantages in greening, which include space saving, light weight, low maintenance, high air purification capacity and unique aesthetic values. However, not much is known about their application under subtropical regions. This study investigated which species that are suitable for use in urban greening under subtropical climate and how they can be utilized.To understand species composition in current moss greening market and estimate the extent of moss exploitation, a survey was conducted based on the data extracted from the online platform Taobao. The top three mosses sold were Leucobryum, Hypnum and Thuidiaceae. A field study was carried out to understand the microhabitats of 12 common moss species in Hong Kong. Meanwhile, preliminary culture of these 12 mosses was initiated in a greenhouse to select potential candidates for further application. Different moss species have their specific distribution according to light, elevation and substrate requirements. Four species showed good growth in the preliminary greenhouse culture, namely Bryum coronatum, Haplocladium microphyllum, Hypnum plumaeforme var. minus and Taxiphyllum taxirameum. They were selected as candidate species for greening.A series of greenhouse cultivation experiments were performed to investigate the growth requirements of mosses on water, growth medium, nitrogen and light. Moss cover increase was generally positively related to irrigation frequency, but too much water resulted in contamination from algae, fungi or cyanobacteria. H. plumaeforme var. minus had the highest area growth among the four species, while H. microphyllum and T. taxirameum had comparable results. B. coronatum produced more propagules after prolonged desiccation. For substrate preference, B. coronatum and H. microphyllum preferred well drained river sand. Addition of nitrogen in the form of NH₄NO₃ did not have positive effects on gametophyte development of the four candidates. Hence nutrient supplement was not suggested to promote moss growth. H. microphyllum and H. plumaeforme var. minus produced similar cover increase under different light treatments, while growth of T. taxirameum was significantly reduced under high irradiation. Rapid light responsive curves also suggested that T. taxirameum had poorer responses to changing light environment. Sufficient sunlight was essential to stimulate sporophyte development in B. coronatum.Four candidate mosses were grown on carriers to produce moss mats that could be directly used in greening. In terms of nutrient solution used, tap water and peat extract supported much better growth than Knop's growth medium on the three pleurocarpous species. Moss mat production using B. coronatum fragments in greenhouse was more viable. A nearly 90% moss mat cover was obtained within three months, through sowing a density of 20 g/m² B. coronatum fragments on a thin layer of growth medium on artificial fleece. Low concentrations (10⁻⁶ M to 10⁻⁸ M) of plant hormones kinetin and gibberellic acid showed slight promotion effects on moss growth while higher concentration resulted in smaller leaf size, slender leaf shape and looser leaf arrangement. Significant enhancement effect was only found in the treatment of 10⁻⁶ M gibberellic acid on H. plumaeforme.城市綠化對減輕城市熱島效應，改善空氣污染以及雨水径流都有著重要的作用。但隨著城市人口越來越密集，大都市能提供給公園等傳統綠化的面積非常有限。近些年，苔蘚作為一種新型綠化材料受到越來越多人的關注。這類平時不太起眼的微小植物在綠化應用中有它自己的優勢，包括強大的空氣淨化以及吸水能力，輕便，節省空間，維護成本低，還有獨特的美觀優勢。本研究主要討論在亞熱帶或者熱帶地區，哪些苔蘚植物適合用作城市綠化，它們的培育條件以及應用方式。通過對淘寶上販賣苔蘚的資料進行收集與分析得到，銷售量最高的三種苔蘚植物分別來自白髮蘚屬（Leucobryum）,灰蘚屬（Hypnum）以及羽蘚科（Thuidiaceae）。苔蘚的銷售量,來源,品種,用途等的總結為中國苔蘚植物的開採利用和保護現狀提供了基本的資料。在亞熱帶城市香港，選取了12種常見的苔蘚植物，詳細地調查了它們的生存環境。野外調查表示不同的苔蘚品種對光照，生長基質種類，海拔高度等的選擇各不相同。經過對這12種苔蘚植物初步的溫室種植後，以下4種表現良好的品種被選出進行之後的培育和應用實驗：蕊形真蘚（Bryum coronatum），細葉小羽蘚（Haplocladium microphyllum），大灰蘚小型變種（Hypnum plumaeforme var. minus）和鱗葉蘚（Taxiphyllum taxirameum）。為了進一步瞭解四種候選苔蘚對水分，生長基質，氮元素以及光照的需求，我們進行了一系列的溫室培育實驗。總的來說，大灰蘚小型變種生長最快，覆蓋度增長也最高。接下來是細葉小羽蘚跟鱗葉蘚，覆蓋度增長不相上下，最後的是蕊形真蘚。 苔蘚覆蓋度的增長速率與澆水頻率成正相關，但太過頻繁會容易導致藻類，藍細菌以及真菌的侵染。在缺水的情況下，蕊形真蘚反而產生更多的側芽繁殖體。在基質實驗中，蕊形真蘚跟細葉小羽蘚偏好透水性好的河沙。 特別是細葉小羽蘚，在75%河沙25%泥炭土的基質中有顯著增強的覆蓋度生長。大灰蘚小型變種跟鱗葉蘚偏好保水性能較好的泥炭土。氮添加實驗結果顯示，不同濃度的硝酸銨溶液都對苔蘚生長沒有顯著促進作用，反而不利於配子體的正常生長，因此不建議添加使用。在不同遮光程度的處理下，細葉小羽蘚和大灰蘚小型變種表現出相似的覆蓋度生長但是不同的光反應曲線。遮光度小於或等於30%都會對鱗葉蘚的生長造成顯著抑制。不同光照條件下重合的光反應曲線也反映出鱗葉蘚對強光照的不適應。充足的光照對蕊形真蘚孢子體的產生至關重要。將苔蘚種植在輕便保水的載體（纖維網布、棕櫚墊、人造毛粘布）上形成苔蘚毯，可以直接應用到綠化中。在完全缺少傳統土壤基質的情況下，用Knop's溶液、泥炭土的浸出液做為營養來源。結果表示在該種情況下苔蘚生長緩慢，Knop's溶液甚至導致苔蘚大面積死亡。使用蕊形真蘚碎片在溫室培育苔蘚毯的方式更為有效。將密度為20 g/m² 的蕊形真蘚碎片均勻地播撒在鋪有薄薄一層土壤基質的人造毛粘布上，3個月過後覆蓋度能達到90%。這種苔蘚廣泛分佈在溫暖的熱帶或亞熱帶地區，繁殖週期快，繁殖能力強，因此有潛力成為一種新型的綠化材料，尤其適應屋頂等光照充足的地方。低濃度的生長激素跟赤黴素 （10⁻⁶ M 和10⁻⁸ M）被證明能促進苔蘚配子體生長。大灰蘚小型變種在10⁻⁶ M赤黴素的作用下覆蓋度顯著提高。Wu, Yuting.Thesis M.Phil. Chinese University of Hong Kong 2019.Includes bibliographical references (leaves 125-149).Abstracts also in Chinese.Title from PDF title page (viewed on 22, December, 2020)