Abstract
The soil microbial community (SMC) provides critical ecosystem services including organic matter decomposition, soil structural formation, and nutrient cycling. Studies suggest plants, specifically trees, act as soil keystone species controlling SMC structure via multiple mechanisms (e.g., litter chemistry, root exudates, and canopy alteration of precipitation). Tree influence on SMC is shaped by local/regional climate effects on forested environments and the connection of forests to surrounding landscapes (e.g., urbanization). Urban soils offer an ideal analog to assess the influence of environmental conditions versus plant species-specific controls on SMC. We used next generation high throughput sequencing to characterize the SMC of specific tree species (Fagus grandifolia [beech] vs Liriodendron tulipifera [yellow poplar]) across an urban–rural gradient. Results indicate SMC dissimilarity within rural forests suggests the SMC is unique to individual tree species. However, greater urbanization pressure increased SMC similarity between tree species. Relative abundance, species richness, and evenness suggest that increases in similarity within urban forests is not the result of biodiversity loss, but rather due to greater overlap of shared taxa. Evaluation of soil chemistry across the rural–urban gradient indicate pH, Ca+, and organic matter are largely responsible for driving relative abundance of specific SMC members.
Highlights
The soil microbial community (SMC) provides critical ecosystem services including organic matter decomposition, soil structural formation, and nutrient cycling
A possible trend in greater species evenness was measured in beech trees in the interior of rural forests compared to the interior of urban and suburban forests (Fig. Sup 1a, p < 0.08)
We observed a similar trend in greater species evenness for beech rural and suburban edge trees compared to urban edge trees Fig. Sup 1b, p < 0.10), and greater species richness in rural and urban compared to suburban beech trees along the forest edge (Fig. Sup 1d, p < 0.07)
Summary
The soil microbial community (SMC) provides critical ecosystem services including organic matter decomposition, soil structural formation, and nutrient cycling. Trees, act as soil keystone species controlling SMC structure via multiple mechanisms (e.g., litter chemistry, root exudates, and canopy alteration of precipitation). Urban forest trees offer the ideal experimental system to evaluate whether natural (i.e., plant) or anthropogenic (i.e., altered environment) factors have the greatest effect on SMC structure and distribution. Wang et al.,[35] found differences in the nitrifying/denitrifying community structure within urban lawns compared to rural farmland soils suggesting a potential decline in ecosystem functionality While these studies provide pivotal evidence indicating potential loss of microbial diversity, they do not consider the influence of abiotic pressures (i.e., urbanization) on plants (i.e., biotic factors) shaping the SMC structure/composition
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