Impacts of experimental flooding on microbial communities and methane fluxes in an urban meadow, baton rouge, louisiana

Abstract

The impacts of extended flooding on microbial communities and their activities in natural and agricultural wetlands have been well-documented, but there is little basis for predicting the responses of urban soil microbial communities to infrequent, short-term flooding. To assess these responses, surface soil samples (0–1 cm) and intact soil cores (10 cm depth) were collected from an urban meadow in Baton Rouge, LA subsequent to an unprecedented flood during August 2016. During the flood, a topographically low region of the meadow (LM) was inundated for at least several days, while an elevated area (upper meadow or UM) was not flooded. Microbial community composition and diversity at each site were assessed for soils collected from cores at various depths over the upper 10 cm before and after 3 days of experimental flooding ex situ. Cores from LM and UM were also used to assess methane fluxes before and after the experimental flooding. The results indicated that methane fluxes differed between LM and UM sites, and that they were affected by flooding. LM cores emitted methane prior to flooding, and rates increased substantially post-flooding; UM cores consumed methane to levels below ambient atmospheric concentrations prior to flooding, but emitted methane post-flooding. In contrast both LM and UM microbial communities were resistant to short-term flooding, with no significant changes observed at either site, or at any depth interval from the surface to 10 cm. However, LM and UM soil communities differed significantly, with distinct distributions of Acidobacteria, Nitrospirae, and Thaumarchaeota among others. Based on responses of soil cores to experimental flooding, the differences between sites in microbial communities did not appear to be residual effects of the August, 2016 flood, but rather appeared to arise from physical, chemical, and biological variables that change along a 4-m elevation gradient. Collectively, the results suggest that the composition and diversity for some urban soils might be insensitive to short-term flooding, but that important biogeochemical processes, e.g., methane fluxes, might respond rapidly.