Quantifying the soil community in green roofs

A 'green roof' is one that has a substrate placed upon it, with the intention of supporting a plant community. Green roofs are a rapidly expanding technology in the UK, because they absorb CO2 and particulates, prevent water run off and insulate the building. They can also enhance local biodiversity by providing habitats for declining plants, pollinating insects and birds. All new developments in major cities like London must now consider green roofs, but there is a complete lack of knowledge regarding the most appropriate way to ensure successful plant community establishment. Even in summers like 2007 and 2008, when water was not limiting, plant establishment is poor. For economic reasons, the most common growing medium used in green roofs is crushed brick, with the addition of 10 or 20% organic matter. The medium is applied dry, so when the roof is constructed soil invertebrates are likely to be absent and the microbial community much impoverished. Our hypothesis is that the lack of 'soil' biota is one of the main reasons why plant establishment is slow and unpredictable. Our principal aims are to 1) characterise the community of soil invertebrates and microbes in roofs of different age, to discover what organisms are present, and 2) to add mixtures of soil bacteria and fungi, to determine if a sustainable microbial community can develop and whether this can enhance invertebrate and plant establishment. Previous projects have established 11 green roofs across London, including five on the halls of residence at Royal Holloway. The roofs vary in age from 1-10 years. This project will sample these roofs to determine the structure of the microbial and invertebrate communities present in the rootzones. Preliminary work suggests that the roofs are not devoid of life, and so it is critical to determine what species are capable of colonising the roofs, how they do this, and over what time scale colonisation occurs. Bacterial and fungal communities will be assessed using phospho lipid fatty acid analysis, a reliable technique that is culture-independent. Soil invertebrates (e.g. mites, nematodes, insects, molluscs) will be extracted and identified to species whenever possible. Our primary CASE partner (Soil Food Web Lab.) will assist and provide expertise in soil community profiling. The microbial community will be manipulated by the addition of bacterial and fungal inoculants, provided by our second CASE partner (Symbio Ltd). This will be done on the roofs at RHUL (which are 1 - 4 y of age) and we will also construct a new roof, with an exact mimic at ground level. By taking this 'bottom-up' approach of augmentation at the base of a food web, we will be able to determine if it is possible to establish a sustainable microbial community, whether this can allow increased invertebrate densities and whether there is a concomitant enhancement of plant establishment and growth. The outcome of this project will be a knowledge of the best practice that can be used to develop sustainable green roofs. Currently, these do not realise their true potential, but there is a pressing need for them to do so, given that green roofs will be a major feature in the development of the London 2012 Olympic complex. A feature of the project, and thus the training provided, is the integration of economic, ecological and analytical principles and the linking of soil ecology to the construction industry. Finding a way of producing sustainable and effective green roofs would vastly improve the quality of life in our cities, through carbon absorption, pollutant reduction, biodiversity enhancement and the psychological benefits to people through their aesthetic appeal.