Long-term storage affects resource availability and occurrence of bacterial taxa linked to pollutant degradation and human health in landscaping materials

Laura Soininen,Mira Grönroos,Marja I Roslund,Aki Sinkkonen

doi:10.1016/j.ufug.2021.127065

Abstract

Man-made landscaping materials form uppermost soil layers in urban green parks and lawns. To optimize effects of landscaping materials on biodiversity, plant growth and human health, it is necessary to understand microbial community dynamics and physicochemical characteristics of the landscaping materials during storage. In the current three-year study, the consequences of long-term storage on biotic and abiotic characteristics of eight commercial landscaping materials were evaluated. We hypothesized that long-term storage results in changes in microbial utilization of various energy sources and the diversity and relative abundance of bacteria with pathogenic or immunomodulatory characteristics. Three-year storage led to remarkable changes in bacterial community composition. Diversity and richness of taxa associated with immune modulation, particularly phylum Proteobacteria and class Gammaproteobacteria, decreased over time. Bacteroidetes decreased while Actinobacteria increased in relative abundance. Functional orthologs associated with biosynthesis of antibiotics and degradation of complex carbon sources increased during storage. Relative abundance of genera containing potential pathogens were mostly constant or decreased with time. Major changes can be explained by tightening competition over lessening resources. Bacterial communities in landscaping materials adjust to absent inflow of carbon and nutrients during storage. The increased signalling of functional orthologs related to degradation of complex carbon sources hints that bacteria dependent on labile carbon and readily available nutrients were outcompeted. This suggests storage reduces plant seedling growth. Long-term storage seems to decrease immunomodulatory potential of landscaping materials, but storage did not enrich pathogens or functional orthologs associated with pathogenicity. We recommend short storage and shelf life of organic landscaping materials.

Highlights

Landscaping materials contain a mixture of microbes, such as bac teria, that cooperate and compete with other microbes and plants
As bacterial communities in landscaping materials strongly reflect nutrient availability and as environmental bacterial communities have a distinctive, well-recognized potential in immunomodulation (Rook et al, 2004; Parajuli et al, 2017; Flandroy et al, 2018), we focused on bacterial community dynamics and prediction of functional orthologs using next-generation sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG)
Shifts detected in our landscaping materials are in accordance with the clas sification by Fierer et al (2007) who identified taxa as having charac teristics of the r- and K-selection strategies; the r-selection strategy refers to fast-growing bacterial species that live in unstable environments, while K-selection refers to slow-growing bacterial species that live in more stable environments

Summary

Introduction

Landscaping materials contain a mixture of microbes, such as bac teria, that cooperate and compete with other microbes and plants. The microbial composition of the environment influences human health, as its microbiological content is mirrored in the human microbiome (Von Hertzen et al, 2011; Nurminen et al, 2018; Gronroos et al, 2019) and the microbial communities in homes (Parajuli et al, 2018; Hui et al, 2019b; Kirjavainen et al, 2019). Urban biodiversity can be increased by urban gardening (Orsini et al, 2013), greening public spaces (Hui et al, 2019a; Puhakka et al, 2019), and utilizing diverse plant communities and landscaping mate rials containing high microbial diversity (Parajuli et al, 2018, 2020)

Methods

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Discussion

Conclusion