COS 46-6 - CANCELLED - Characterizing Suburban Residential Soils: What Factors Drive Microbial Community Assembly and Function?

Abstract: Microbial communities are key regulators in soil processes including carbon sequestration and nutrient cycling. Factors influencing microbial community structure and function, such as disturbance regimes, nutrient availability, and soil moisture, have been well-studied in natural and agricultural systems. Urban soil microbiomes have been largely overlooked. Emerging studies of urban soils and their microbiota often focus on large urban-to-rural gradients, leaving many questions about microbial ecology at smaller scales and in patchier environments still to be explored. Our study seeks to fill this knowledge gap. We sampled soil across 47 yards in a southern California suburban neighborhood, and measured soil characteristics including bulk density, moisture, pH, inorganic nitrogen, and total carbon and nitrogen. We measured microbial community characteristics including respiration, extracellular enzyme activity, abundance, and composition via 16S/ITS sequencing. We also sampled soil from a natural preserve abutting the neighborhood to understand how managed residential soils compare to undeveloped soils. We hypothesized that there will be a small signal of soil/microbial succession over time after the houses were initially developed, but that subsequent landscaping choices and homeowner management (e.g. irrigation and fertilization) will be the dominant drivers of microbial composition and function.

We used correlation tests to determine whether soil and microbial variables significantly responded to “time since development”. We found that as properties age after development, bulk density and soil pH decrease. However, microbial abundance and respiration responded more to soil moisture and nutrient content, rather than time, suggesting that microbial communities in residential soils are responding to a more stochastic disturbance and nutrient-availability regime rather than following a consistent successional trajectory. Samples were also split into landscaping categories of “turfgrass” and “mixed vegetation” to determine whether landscaping choices affected soil and microbial characteristics. Mixed vegetation included any non-turfgrass plants. Variation was high among properties and, overall, vegetation type did not have a significant effect on microbial abundance, respiration, bulk density, or pH. Turfgrass soils did have higher gravimetric water content because of more intense irrigation by homeowners. Nitrate and ammonium content were also higher in turfgrass, likely due to increased fertilization by homeowners and exposure to dog urine. Preliminary results overall suggest that suburban residential yards are highly heterogeneous. Understanding this heterogeneity, and identifying which factors most strongly impact microbial communities and nutrient fluxes, will allow for better management of urban greenspaces to conserve resources and promote sustainability.