Effects of Urban Green Infrastructure Designs on Soil Bacterial Community Composition and Function

Green infrastructures (GIs) are environmental designs mainly used to treat urban stormwater runoff pollution. The influences of green infrastructure designs are associated with the bacteria composition and diversity in their soils. This study evaluated the effects of GI design on the composition and function of urban soil bacterial communities in Wuhan, China. GI designs were divided into five different types: engineered (road bioswales, rain gardens, and sunken green spaces) and non-engineered (conventional road greenbelts and urban lawns) designs. The engineered soil combined with the connectivity to urban runoff of the GI design can have strong influences on bacterial community composition and function. Across the five GI design types, we found that the composition of bacterial communities was dominated by Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria at the phylum level. The relative abundance of Proteobacteria and Bacteroidetes in the engineered designs was significantly higher than the non-engineered designs and was highest in road bioswales. We detected nine predominant ecological function groups related to the carbon (3 groups) and nitrogen (6 groups) cyclings, with their relative abundance in engineered soils significantly higher than those in non-engineered soils, especially in road bioswales and sunken green spaces. Road bioswales (RBS), with direct connection to urban runoff from street, had the highest denitrification enzyme activity (DEA). DEA of green infrastructures was highly correlated with soil organic carbon, moisture and total nitrogen. Road bioswales appear to function as denitrification hotspots and have higher potential denitrification than other GI designs.