OOS 24-3 - Testing subsidy-stress effects of saltwater intrusion on microbial processing of carbon and nutrients in freshwater wetland soils

Wednesday, August 10, 2016: 2:10 PM
Grand Floridian Blrm G, Ft Lauderdale Convention Center
Shelby Servais1, Benjamin J. Wilson1, Viviana Mazzei1, Evelyn E. Gaiser2, John S. Kominoski3, Tiffany G. Troxler4 and Sean P. Charles3, (1)Biological Sciences, Florida International University, Miami, FL, (2)Southeast Environmental Research Center (SERC), Florida International University, Miami, FL, (3)Florida International University, Miami, FL, (4)Southeast Environmental Research Center, Florida International University, Miami, FL

Carbon (C) cycling in soils is fundamentally linked to the metabolism of microbial communities. Saltwater intrusion into coastal wetlands with sea level rise (SLR) will increase salinity (stress), and marine-derived nutrient subsidies (phosphorus, P; sulfur S) with uncertain effects on microbial activities and biogeochemical processes. Freshwater coastal wetlands of the Florida Everglades are particularly vulnerable to increases in salinity and P due to reductions in freshwater availability and extreme P-limitation. Our objective was to understand how soil microbial extracellular enzyme activities (EEAs) and ecosystem respiration (ER) differentially respond to marine water salinity and elevated P to affect soil C balance and nutrient acquisition in freshwater sawgrass peat soils.  Using a 2 ´ 2 factorial design in experimental wetland mesocosms, we treated sawgrass peat cores (38 ´ 53 ´ 40 cm) with ambient and elevated levels of salinity (+7 ppt) and P (2500 μg L-1). During initial exposure to treatment conditions (52 d), we measured C- and nutrient-based EEAs and ER in surficial soils to assess sensitivity to the subsidy of P and stress of salinity.


Enzyme activities decreased with elevated salinity for acid phosphatase (AKP), arylsulfatase (ARS), beta glucosidase (BG) (2-3 ×lower than ambient; ANOVA, P < 0.05). However, elevated salinity and P combined do not appear to suppress EEAs relative to ambient (P > 0.05). Salinity and P did affect cellulase activities (CEL). Phosphorus potentially mediated suppression of enzyme activity with increased salinity during initial exposure. The C:P stoichiometry of EEAs (BG+CEL:AP) approached global averages of 1:1 in elevated P treatments, suggesting that P subsidies can balance freshwater microbial demands for C and P under elevated and ambient salinity exposure. Soil ER was not altered after 52 d exposure to elevated salinity and P. Early exposure to elevated salinity suppresses microbial enzyme function; however, subsidies of P have the potential to mediate the stressful effect.