Multifunctionality is affected by interactions between green roof plant species, substrate depth, and substrate type

Abstract

SummaryGreen roofs provide ecosystem services through evapotranspiration and nutrient cycling that depend, among others, on plant species, substrate type, and substrate depth. However, no study has assessed thoroughly how interactions between these factors alter ecosystem functions and multifunctionality of green roofs. We simulated some green roof conditions in a pot experiment. We planted 20 plant species from 10 genera and five families (Asteraceae, Caryophyllaceae, Crassulaceae, Fabaceae, and Poaceae) on two substrate types (natural vs. artificial) and two substrate depths (10 cm vs. 30 cm). As indicators of major ecosystem functions, we measured aboveground and belowground biomasses, foliar nitrogen and carbon content, foliar transpiration, substrate water retention, and dissolved organic carbon and nitrates in leachates. Interactions between substrate type and depth strongly affected ecosystem functions. Biomass production was increased in the artificial substrate and deeper substrates, as was water retention in most cases. In contrast, dissolved organic carbon leaching was higher in the artificial substrates. Except for the Fabaceae species, nitrate leaching was reduced in deep, natural soils. The highest transpiration rates were associated with natural soils. All functions were modulated by plant families or species. Plant effects differed according to the observed function and the type and depth of the substrate. Fabaceae species grown on natural soils had the most noticeable patterns, allowing high biomass production and high water retention but also high nitrate leaching from deep pots. No single combination of factors enhanced simultaneously all studied ecosystem functions, highlighting that soil–plant interactions induce trade‐offs between ecosystem functions. Substrate type and depth interactions are major drivers for green roof multifunctionality.

Phosphate Leaching from Green Roof Substrates—Can Green Roofs Pollute Urban Water Bodies?

“…Due to increasing problems with stormwater management in urban areas, the total area of green roofs is going to rise in the future [22,23]. Extensive green roofs have thin substrate layers and need little maintenance, while intensive green roofs have thicker substrates and require more maintenance [24].…”

Wind drives drought responses of green roof vegetation in two substrates

“…The provision of ecosystem services by green roofs may result from complex interactions between substrate type, substrate depth, and plant species, and these interactions probably lead to trade-offs between services [5]. However, substrate manipulations are often limited by the weight-loading capacity of the roof [6].…”

“…This multifunctionality in delivery of ecosystem services by green roofs is improved by biological diversity of the roof vegetation [3]. Green roofs are however harsh environments, where the negative effects of drought, temperature extremes, radiation, air pollution, and wind on vegetation performance are amplified by the shallow and porous substrate low on organic matter used on extensive green roofs [2, 4, 5, 8]. The natural consequence of this green roof construction is limited water availability during prolonged drought, particularly when using water-demanding species [8, 9, 10].…”

Role of substrate properties in the provision of multifunctional green roof ecosystem services

“…To better understand these trade-offs, while information on the links between components of a green roof substrate and the functions or services it fulfills remains fragmented, studies that have sought to cross just two of these components are rare. Until recently (Dusza et al, 2017), no study had evaluated the influence of interactions between substrate depth, substrate composition, and plant species on any of the functions or services of a green roof (Figure 1). In 2015, Lundholm was the first author to explicitly use the term "multifunctionality" in the context of green roofs.…”

“…Lundholm considered three types of treatment in relation to the desired services: the least and most effective for a given service, as well as those with the highest multifunctionality index. This approach is very innovative in the disciplinary field of green roofs and calls for more multifunctionality studies while we now know that substrate-plant interactions induce trade-offs between ecosystem functions, and that substrate type and depth interactions are major drivers for green roof multifunctionality (Dusza et al, 2017).…”