COS 166-5 - Waterlogging drives shifts in the stoichiometry and concentrations of mineral bound and soluble soil C, N and P

Background/Question/Methods

With climate change, much of the world will experience increased flooding, intensifying periods of waterlogging when the soil is saturated. Under waterlogging, the relatively protected mineral-associated soil carbon (C), nitrogen (N), and phosphorus (P) may be destabilized by lower redox conditions, releasing these substrates into their respective soluble pools. Yet, C, N, P are not expected to respond to flooding in the same way, such that soluble C, N, and P concentrations and stoichiometry may change with unknown consequences for microbial activity. Shifts in microbial stoichiometry and retention of C, N, and P may affect the post-flood fate of both soluble and mineral-associated C, N, and P. Understanding how flooding impacts the interactions between the destabilization of mineral-associated C, N and P and the subsequent shifts in soluble substrates and microbial activity can inform predictions of retention or losses of C, N and P following waterlogging. We used a laboratory incubation approach that manipulated waterlogging duration to determine if mineral-associated and soluble C, N and P stoichiometry and concentrations are maintained or altered during and after waterlogging events. Soil incubations were held under standing water for 0.5 hour, 24 hours, or 1 week, followed by air-drying to control moisture conditions.

Results/Conclusions

To understand the exchanges of C, N and P between different pools during flooding, we compared changes in soluble and mineral-associated soil C, N and P as well as impacts on microbial exo-cellular enzymes. Preliminary results indicate that mineral-associated C, N and P is sensitive to water logging, where mineral-associated C increased after waterlogging under the longest flood duration, while mineral-associated P decreased but only under the shortest flood duration. At the same time, soluble organic C increased approximately 35% even under the shortest duration (p< 0.001) and organic N decreased approximately 80% under all waterlogging durations (p< 0.001). In contrast, P showed a more dynamic response increasing at 0.5 hour and 1 week but not at 24 hours. We further found that microbial enzyme activity increases with increasing available C and P resulting from waterlogging. By exploring the combined response of mineral-bound and soluble C, N, and P as well as microbial responses to water logging, we can better understand how different flood scenarios will impact soil C, N and P dynamics.