A research article written by Laura Soininen, Mira Grönroos, Marja Roslund and Aki Sinkkonen has been published in Urban Forestry & Urban Greening. Surface layers in urban green areas consist of landscaping materials, which could potentially be used for immunomodulation and for increasing biodiversity in urban microbial communities in addition to plant growth. Therefore, it is important to understand microbial community dynamics and physicochemical characteristics in the substrates during storage. This three-year study evaluated the consequences of long-term storage on biotic and abiotic characteristics of eight commercial landscaping materials. The bacterial communities were determined using next-generation sequencing and their functional orthologs were predicted based on metabolic genes in the metagenome. Long-term storage was expected to change the microbial utilization of various energy sources, and alter diversity and relative abundance of health-associated bacteria.
As expected, diversity and relative abundance of taxa potentially beneficial to health, such as phylum Proteobacteria and class Gammaproteobacteria, decreased over storage. Relative abundance of genera containing potential pathogens mostly decreased or stayed constant. Biosynthesis of antibiotics and degradation of complex carbon sources increased over storage. These changes may be explained by competition over lessening resources.
Long-term storage seems to decrease immunomodulatory potential of landscaping materials, but not enrich pathogens. As a results of this study, we recommend short storage time for organic landscaping materials when aiming to increase biodiversity and human health in cities.