Forestry- and agriculture-derived materials as potential bacterial supplements in immunomodulatory urban greening

Decreased exposure to environmental microbes among urbanites is generally thought to contribute to the high incidence of several immune-mediated diseases. Urban landscaping materials that provide microbiological diversity and contain health-associated microbes, such as proteobacterial and mycobacterial taxa, could modulate the risk of the immune-mediated diseases. The aim of the current study was to develop soils that contain health-associated microbiota and are suitable for urban landscaping. Therefore, the potential of forestry- and agriculture-derived supplements in urban greening was investigated. Commercially available, peat-based lawn soil (standard substrate) was enriched with boreal forestry side streams (conifer needles, cones, pine bark, alnus leaves, moss debris, reed and manure), moss or side-stream based products (biochar, composted agricultural waste). The microbial communities of the standard and enriched substrates were followed in two year-long studies in which sod and grass were grown outdoors and indoors. Moss, conifer needles and reed retainded and increased the relative abundance of the phylum Proteobacteria and its classes, while Alnus litter and conifer needles supported the relative abundance of Mycobacterium. Temporal shifts in the relative abundance and richness of previously health-associated bacteria were evident. The method of enriching lawn soil with side streams appears to elicit desired shifts in health-associated microbial taxa. The results indicate that several agricultural and forestry side streams are suitable for shaping health-associated microbiota in commercially available soil. Further studies to explore the potential of side streams in immunomodulatory urban greening are recommended.