School of Ecosystem and Forest Sciences, Faculty of Science, The University of Melbourne, 500, Yarra Boulevard, Richmond, Victoria 3121, Australia.
School of Ecosystem and Forest Sciences, Faculty of Science, The University of Melbourne, 500, Yarra Boulevard, Richmond, Victoria 3121, Australia.
Sci Total Environ. 2023 Sep 1;889:164043. doi: 10.1016/j.scitotenv.2023.164043. Epub 2023 May 13.
Green roofs are a promising engineered ecosystem designed to reduce stormwater runoff and restore vegetation cover in cities. Plants can contribute to rainfall retention by rapidly depleting water in the substrate, however, this increases the risk of plant drought stress. This study determined whether lower plant density or preferentially redirecting rainfall to plants on green roofs could reduce drought stress without reducing rainfall retention. Plant density was manipulated, and metal structures were installed above the substrate surfaces to redirect the flow of rainwater towards plants (runoff zones). Green roof modules were used to test three plant density treatments: unplanted, half-planted (10 plants/m) and fully-planted (18 plants/m), and two runoff zone treatments which were installed in unplanted and half-planted modules. It was expected that 1) green roofs with greater plant density would experience more drought stress (i.e., lower leaf water status), and 2) green roofs with runoff zones would show higher ET and hence retention compared with those without runoff zones, as water will be directed to plants (run-on zones), facilitating growth. Contrary to the hypothesis, evapotranspiration (ET) and rainfall retention were similar for half-planted and fully-planted modules, such that ∼82 % of applied rainfall was retained. While both vegetation treatments dried out the substrates before rainfall was applied, the fully-planted modules dried out quicker and showed significantly lower leaf water status than half-planted modules. This indicates that planting at lower density may reduce plant drought stress, without reducing rainfall retention. Installing runoff zones marginally reduced ET and rainfall retention, likely due to shading by the runoff zone structures reducing evaporation from the substrate. However, runoff also occurred earlier where runoff zones were installed as they likely created preferential flow paths that reduced soil moisture and therefore ET and retention. Despite reduced rainfall retention, plants in modules with runoff zones showed significantly higher leaf water status. Reducing plant density therefore represents a simple means of reducing plant stress on green roofs without reducing rainfall retention. Installing runoff zones on green roofs is a novel approach that could reduce plant drought stress, particularly in hot and dry climates, albeit at a small cost of reduced rainfall retention.
绿色屋顶是一种有前途的工程生态系统，旨在减少城市雨水径流并恢复植被覆盖。植物可以通过迅速耗尽基质中的水分来促进雨水截留，然而，这增加了植物干旱胁迫的风险。本研究旨在确定较低的植物密度或优先将雨水引向绿色屋顶上的植物是否可以在不减少雨水截留的情况下降低干旱胁迫。通过操纵植物密度，并在基质表面上方安装金属结构来将雨水流向植物（径流区）来实现。使用绿色屋顶模块来测试三种植物密度处理：无植物、半种植（每平方米 10 株）和全种植（每平方米 18 株），以及两种径流区处理，分别安装在无植物和半种植模块中。预计：1）植物密度较高的绿色屋顶将经历更多的干旱胁迫（即较低的叶片水分状况），2）有径流区的绿色屋顶的蒸散量（ET）会更高，因此与没有径流区的相比，保留率会更高，因为水会被引导到植物（径流区），从而促进植物生长。与假设相反，半种植和全种植模块的蒸散量（ET）和雨水截留率相似，因此约 82%的应用降雨量被截留。虽然两种植被处理在应用降雨前都使基质变干，但全种植模块比半种植模块更快地变干，并且叶片水分状况明显低于半种植模块。这表明以较低的密度种植可能会降低植物的干旱胁迫，而不会降低雨水截留率。安装径流区略微降低了 ET 和雨水截留率，可能是由于径流区结构的遮荫减少了基质蒸发。然而，由于径流区可能会创建优先流路径，从而降低土壤水分，因此 ET 和保留率也会降低，因此在安装径流区的地方，径流也更早发生。尽管雨水截留率降低，但安装径流区的模块中的植物的叶片水分状况明显更高。因此，降低植物密度是一种简单的方法，可以降低绿色屋顶上植物的压力，而不会降低雨水截留率。在绿色屋顶上安装径流区是一种新颖的方法，可以降低植物干旱胁迫，特别是在炎热干燥的气候下，尽管会降低少量的雨水截留率。
