Flooding transforms the soil environment, impacting small-scale controls on mineral associated carbon (C), nitrogen (N) and phosphorus (P) stabilization and mobilization. Yet during ood events, mineral associated C, N, and P may not respond in the same way, such that soluble C, N, and P concentrations and stoichiometry may change with unknown consequences for microbial activity. Using a laboratory incubation approach, we investigated how ooding impacts C, N, and P pool distribution and microbial activity across a 1-week ood event and after drying. We found that all three mineral associated pools responded dynamically to ooding, increasing and decreasing throughout the ood with a net increase of 5.9% in mineral associated C and 32.5% decrease in residual P. However, mineral associated C, N, and P each shifted at different temporal points, indicating that they are likely responding to separate destabilization mechanisms working at different temporal scales. The soluble C and N responses to ooding contrasted the mineral associated pool's response, increasing by 57% and decreasing by 72% respectively at the beginning of the ood which remained post-ood. However, soluble P behaved more similarly to the mineral associated pool. The microbial community maintained and even increased their exo-cellular activity throughout the ood period, responding most strongly to changes in available P. Our research demonstrates that the mineral associated pool is sensitive to short-term ooding altering the composition and quantity of water extracted compounds and microbial activity.

No abstract

<p>With climate change, much of the world will experience devastating shifts in weather patterns like increased flooding, intensifying periods of soil saturation. Soil carbon (C), nitrogen (N) and phosphorus (P) cycles are sensitive to changes in soil saturation, where exchange between the mineral-bound and the soluble bioavailable pools can occur with increases in moisture content. With soil saturation, C, N, and P may be mobilized either through greater diffusion or reduced conditions that cause desorption of mineral-bound C, N and P into their respective soluble pools. De-sorption, resorption and diffusion dynamics of C, N, and P may or may not reflect the stoichiometry of the mineral bound pool. Changes in bioavailable soluble C, N and P that could occur with soil saturation and drying may cause unknown consequences for microbial biomass C:N:P. With increases in soil moisture, simultaneous changes in both substrate stoichiometry and microbial growth may occur that impact microbial biomass stoichiometry.  Such changes in microbial stoichiometry and microbial retention of C, N, and P may affect the post-flood fate of soluble C, N, and P. Understanding how releases in mineral bound C, N and P alter the bioavailable C:N:P and how this in turn impacts microbial activity and accumulation of these substrates can inform predictions of retention or losses of C, N and P following soil saturation events.</p><p>To determine if mineral-bound, soluble and microbial biomass stoichiometry is maintained or altered during and after soil saturation events, we used a laboratory incubation approach with manipulated soil saturation and duration. Soil incubations were maintained at three water-holding capacity (WHC) levels: 20% (control), 50%, (moderate) and 100% (severe). We maintained the moderate and severe water-logging treatments for  0.5 h, 24 h, 1 week, followed by air-drying to 20% WHC to examine the influence of flood duration. To understand the exchanges of C, N and P between different pools during flooding, we compared changes in soluble and mineral bound soil C, N and P and impacts on microbial C, N, and P exo-cellular enzymes, and microbial biomass C:N:P. Preliminary results indicate that greater soil moisture content increases soluble P and that the 24 hour flood period captures shifts in the mineral bound P pool that do not remain for the longer flood period (1 week). Enzyme activity similarly reflects an increase in microbial activity in the soil held at 50% and 100% moisture content for 24 hours. We also discuss how soil moisture levels and flood duration impact soluble and mineral bound C relative to P, and how microbial biomass C:N:P tracks these fractions. By exploring the combined response of mineral-bound and soluble C, N, and P to variation in soil saturation, we can better understand how different flood scenarios will impact soil C, N and P retention.</p>

Flooding transforms the soil environment, impacting small-scale controls on mineral associated carbon (C), nitrogen (N) and phosphorus (P) stabilization and mobilization. Yet during flood events, mineral associated C, N, and P may not respond in the same way, such that soluble C, N, and P concentrations and stoichiometry may change with unknown consequences for microbial activity. Using a laboratory incubation approach, we investigated how flooding impacts C, N, and P pool distribution and microbial activity across a 1-week flood event and after drying. We found that all three mineral associated pools responded dynamically to flooding, increasing and decreasing throughout the flood with a net increase of 5.9% in mineral associated C and 32.5% decrease in residual P. However, mineral associated C, N, and P each shifted at different temporal points, indicating that they are likely responding to separate destabilization mechanisms working at different temporal scales. The soluble C and N responses to flooding contrasted the mineral associated pool’s response, increasing by 57% and decreasing by 72% respectively at the beginning of the flood which remained post-flood. However, soluble P behaved more similarly to the mineral associated pool. The microbial community maintained and even increased their exo-cellular activity throughout the flood period, responding most strongly to changes in available P. Our research demonstrates that the mineral associated pool is sensitive to short-term flooding altering the composition and quantity of water extracted compounds and microbial activity.