How Does Prolonged Flooding Alter Microbial Carbon and Nutrient Demands Across Coastal Terrestrial–Aquatic Interfaces in the Great Lakes?
Donnie Day1* (email@example.com), Michael Weintraub1, Vanessa Bailey2, Kennedy Doro1, Daryl Moorhead1, Kaizad Patel2, Allison Myers-Pigg3
1University of Toledo, Toledo, OH; 2Pacific Northwest National Laboratory, Richland, WA; 3Marine and Coastal Research Laboratory, Pacific Northwest National Laboratory, Sequim, WA
Although soil microbes respond rapidly to environmental stimuli, it is unclear how flooding affects carbon (C) availability and turnover rates in coastal ecosystems of the Great Lakes region. As part of the Coastal Observations, Mechanisms, and Predictions Across Systems and Scales–Field, Measurements, and Experiments (COMPASS-FME) pilot project, this study aims to disentangle the effects of prolonged flooding on soil microbes and their mechanisms for adaptation. Generally, C availability and turnover rates are limited by extracellular enzyme activity and nutrient availability; however, dominant controls are expected to shift from nutrient to oxygen limitations under hypoxic conditions. Moreover, the team predicts oxygen limitations will reduce dissolved organic carbon (DOC) availability and microbially derived nutrients by inhibiting enzyme activities. To test this hypothesis, researchers conducted a microcosm experiment on soils from three zones across a terrestrial–aquatic interface (TAI) at Old Woman Creek, OH. This site spans an upland deciduous forest, a water-stressed deciduous forest transition, and an inundated wetland. Soils were subjected to nonflooded (oxic) and flooded (hypoxic) treatments and destructively harvested on days 0, 7, 21, and 55 to determine C turnover via C mineralization, potential rates of microbial C and C, nitrogen (N), and phosphorus (P) acquiring enzyme activities, and extractable C, N, and P pools. Results showed oxygen limitations immediately decreased C turnover and DOC in upland and wetland soils (p<0.05) but not in transition soils. Interestingly, C mineralization increased episodically in both flooded wetland and transition soils, corresponding to declines in microbial C and increased DOC and nitrate; however, this DOC was quickly mineralized in flooded wetland soils but not in flooded transition soils. Enzyme stoichiometric analysis revealed that polymeric carbon catalysis remained constant regardless of TAI location or treatment, indicating that slow exoenzymes turnover provided a lag in biogeochemical responses. Overall, these results suggest a shift from nutrient to oxygen limitations occurs within days across the TAI in response to flooding, but increased microbial turnover is responsible for episodic increases of DOC, nutrient availability, and C turnover. Therefore, further research is required to determine the effects of hypoxia on microbial communities and the accessibility of soil C sources of varying chemical quality to better predict how microbial responses to flooding affect C and nutrient cycling across TAIs.