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SFS Annual Meeting

Thursday, May 23, 2019
11:00 - 12:30

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11:00 - 11:15: / 254 B AN IN SITU TEST SUPPORTS STRONG NEGATIVE ALGAL PRIMING OF LEAF DECOMPOSITION IN A LENTIC ECOSYSTEM

5/23/2019  |   11:00 - 11:15   |  254 B

AN IN SITU TEST SUPPORTS STRONG NEGATIVE ALGAL PRIMING OF LEAF DECOMPOSITION IN A LENTIC ECOSYSTEM During plant litter decomposition, periphytic algae can stimulate decomposer microbes and enhance decomposition through positive priming effects (PEs). Despite this potential importance of algae, the direction and magnitude of algal PEs in aquatic settings remain poorly tested, with only a limited number of studies that have shown mixed results. We tested algal PEs during decomposition of cattail litter (Typha domingensis) in a lake littoral zone using floating experimental mesocosms under extended light versus dark conditions. Light increased algal biomass and rates of algal production (P<0.001), which in turn stimulated fungal growth rates (P<0.001). Despite increases in algal-stimulated fungal growth, light significantly reduced fungal biomass (P<0.001), carbon-acquiring degradative enzymes ?-glucosidase, ?-xylosidase, and phenol oxidase (P<0.001), and litter mass loss rates (P<0.001). These findings of negative PEs support prior investigations conducted in a lotic ecosystem, where periphytic algae decoupled fungal activity from litter decomposition, likely by providing labile carbon invested in growth versus recalcitrant litter degradation. If common, such microbial interactions have important implications for our understanding of litter decay processes within aquatic ecosystems as well as flow of energy and nutrients to upper trophic levels.

Kevin Kuehn (Primary Presenter/Author), The University of Southern Mississippi, kevin.kuehn@usm.edu;


Halvor Halvorson (Co-Presenter/Co-Author), University of Southern Mississippi, Halvor.Halvorson@usm.edu;


Robert Findlay (Co-Presenter/Co-Author), University of Alabama, rfindlay@ua.edu;


Steven Francoeur (Co-Presenter/Co-Author), Eastern Michigan University, sfrancoeu@emich.edu;


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11:15 - 11:30: / 254 B SOY-BASED DENITRIFICATION POTENTIAL: CROP LITTER TRANSPORT, BREAKDOWN AND ASSOCIATED BIOGEOCHMEICAL PROCESSES IN MISSISSIPPI DELTA FRESHWATER AGROECOSYSTEMS

5/23/2019  |   11:15 - 11:30   |  254 B

SOY-BASED DENITRIFICATION POTENTIAL: CROP LITTER TRANSPORT, BREAKDOWN AND ASSOCIATED BIOGEOCHMEICAL PROCESSES IN MISSISSIPPI DELTA FRESHWATER AGROECOSYSTEMS Freshwater ecosystem function in agricultural landscapes is likely influenced by crop-derived detritus entering freshwater habitats. We estimated litter transport and breakdown rates of soybean litter within a stream bayou located within the Lower Mississippi River Basin (LMBR). Additionally, we performed sediment core incubations with and without soybean litter bags collected from the bayou over time to estimate effects of soybean litter on respiration and denitrification rates throughout the decomposition process. Preliminary results indicate that: 1) soybean detritus entered aquatic habitats from late October through December; 2) detritus decomposed rapidly with most of the material gone in 48 days; and 3) detritus increased respiration and denitrification rates above background sediment rates during the decomposition process. Our results document transport of soybean litter into freshwater habitats and confirm that this labile material can contribute to the timing and magnitude of low dissolved oxygen impacts associated with post-harvest conditions. However, soybean litter also enhances the potential for bayou habitats to remove excess N by stimulating denitrification as surface water moves through low-gradient drainage networks typical of the LMRB landscape.

Jason M. Taylor (Primary Presenter/Author), USDA, Agricultural Research Service, National Sedimentation Lab, jason.taylor@ars.usda.gov;


Richard Lizotte (Co-Presenter/Co-Author), USDA, Agricultural Research Service, National Sedimentation Lab , richard.lizotte@ars.usda.gov;


Sam Testa (Co-Presenter/Co-Author), USDA, Agricultural Research Service, National Sedimentation Lab , sam.testa@ars.usda.gov;


Halvor Halvorson (Co-Presenter/Co-Author), University of Southern Mississippi, Halvor.Halvorson@usm.edu;


Kevin Kuehn (Co-Presenter/Co-Author), The University of Southern Mississippi, kevin.kuehn@usm.edu;


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11:30 - 11:45: / 254 B TEMPERATURE EFFECTS ON SHREDDER AND MICROBIAL PROCESSING OF LEAF LITTER IN STREAMS DEPEND ON SEASON AND LITTER TYPE

5/23/2019  |   11:30 - 11:45   |  254 B

TEMPERATURE EFFECTS ON SHREDDER AND MICROBIAL PROCESSING OF LEAF LITTER IN STREAMS DEPEND ON SEASON AND LITTER TYPE Microorganisms and shredding invertebrates are key drivers of allochthonous carbon processing in streams but contribute to different fates of carbon (CO2 vs. storage/transport of fine particles). These groups may respond differently to temperature: while microbial processing is predicted to increase with temperature following the Metabolic Theory of Ecology (MTE), shredder contributions to litter breakdown may be lower than predicted by MTE as temperatures rise due to physiological constraints. To investigate the effects of temperature on shredder and microbial carbon processing, we conducted twelve 2-month incubations of Rhododendron maximum and Acer rubrum leaves across a stream temperature gradient at the Coweeta Hydrologic Laboratory. Microbial breakdown rates were positively related to temperature in both warmer and cooler months, roughly following MTE. Shredder processing increased with temperature in warmer months but decreased with temperature in cooler months, illustrating the importance of seasonal phenology in dictating shredder carbon processing. Consistently higher activation energy of Rhododendron vs. Acer breakdown indicates higher temperature sensitivity of recalcitrant vs. labile carbon. Future work will focus on quantifying the effects of organismal life history and litter quality on carbon allocation to CO2, storage, and transport as temperatures rise.

Carolyn Cummins (Primary Presenter/Author), The University of Georgia, carolynsc1225@gmail.com;


Amy Rosemond (Co-Presenter/Co-Author), University of Georgia, rosemond@uga.edu;


Phillip Bumpers (Co-Presenter/Co-Author), Odum School of Ecology, University of Georgia, bumpersp@gmail.com;


Nathan Tomczyk (Co-Presenter/Co-Author), University of Georgia, nathan.tomczyk@gmail.com;


Jonathan Benstead (Co-Presenter/Co-Author), The University of Alabama, jbenstead@ua.edu;


Vlad Gulis (Co-Presenter/Co-Author), Coastal Carolina University, vgulis@coastal.edu;


Seth Wenger (Co-Presenter/Co-Author), University of Georgia, sethwenger@fastmail.fm;


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11:45 - 12:00: / 254 B DIVING INTO MURKY WATERS - EFFECTS OF BROWNIFICATION ON STREAM BIOFILM QUALITY, FUNCTIONING AND STRUCTURE

5/23/2019  |   11:45 - 12:00   |  254 B

DIVING INTO MURKY WATERS - EFFECTS OF BROWNIFICATION ON STREAM BIOFILM QUALITY, FUNCTIONING AND STRUCTURE Colour of surface waters has darkened throughout the northern hemisphere due to alteration of the quantity and quality of terrestrially-produced dissolved organic carbon (DOC). Forestry actions intensify ‘brownification’ by soil modification and enhance light availability via removal of riparian canopy. We used near-natural stream mesocosms to test experimentally, whether brownification and canopy removal affect the nutritional quality, functioning and structure of stream biofilm communities. Elevated DOC resulted in significantly higher bacterial production, likely fuelled by excess C, as we detected a simultaneous increase in biofilm respiration. Algal productivity and amount of essential fatty acids (EPA and DHA) decreased drastically and terrestrially-produced low-quality fatty acids (LSAFA) increased with brownification. Canopy removal mainly attenuated the effects of elevated DOC as algae benefitted from less limited light conditions. Overall, our results indicate that brownification cause a strong shift towards heterotrophy in system metabolism. Changes that occur in stream biofilm are likely to cascade higher up in stream food webs and downstream in a stream network. Thus, understanding the consequences of brownification is crucial for more effective water quality and carbon cycling management.

Maria Rajakallio (Primary Presenter/Author), University of Oulu, maria.rajakallio@oulu.fi;


Jussi Jyväsjärvi (Co-Presenter/Co-Author), Ecology and Genetics Research Unit, University of Oulu, Finland, jussi.jyvasjarvi@oulu.fi;


Sami Taipale (Co-Presenter/Co-Author), University of Jyväskylä, sami.taipale@jyu.fi;


Pauliina Louhi (Co-Presenter/Co-Author), Natural Resources Institute Finland, pauliina.louhi@luke.fi;


Timo Muotka (Co-Presenter/Co-Author), Ecology and Genetics Research Unit, University of Oulu, Finland, timo.muotka@oulu.fi;


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12:00 - 12:15: / 254 B AMONG AND WITHIN-SPECIES FUNCTIONAL VARIABILITY OF AQUATIC AND TERRESTRIAL MACRO-DETRITIVORES

5/23/2019  |   12:00 - 12:15   |  254 B

AMONG AND WITHIN-SPECIES FUNCTIONAL VARIABILITY OF AQUATIC AND TERRESTRIAL MACRO-DETRITIVORES Predicting consumption rate variability with other traits could help to scale up information from individuals to ecosystems. While body mass appears to be the most informative trait to explain consumption rate among species, recent studies suggest it could be less informative among individuals of a same species. We tested this hypothesis using aquatic and terrestrial macro-detritivores, with an experiment assessing litter consumption rate repeatedly for each individual. This design allows to partition the consumption rate variability among species and among individuals and to test the explanatory power of body mass to predict consumption rate at both levels, as well as to test the generality of our results. We estimated 35% of variability owned to individuals and 53% to species. Body mass explained 38% of among-species variability, but only 4% of variability found among individuals within species. Yet, almost 38% of variability found among individuals was repeatable and thus could be explained by phenotypic traits. These results validate our hypothesis, which appears to generalize across aquatic and terrestrial macro-detritivores. We suggest which phenotypic traits beyond body mass could be useful to unravel consumption rate variability across biological levels of organization.

Thibaut Rota (Primary Presenter/Author), EcoLab, Université de Toulouse, CNRS, France, thibaut.rota@univ-tlse3.fr;


Benjamin Pey (Co-Presenter/Co-Author), EcoLab, Université de Toulouse, CNRS, France, benjamin.pey@ensat.fr;


Eric Chauvet (Co-Presenter/Co-Author), EcoLab, Université de Toulouse, CNRS, France, eric.chauvet@univ-tlse3.fr;


Antoine Lecerf (Co-Presenter/Co-Author), EcoLab, Université de Toulouse, CNRS, France, antoine.lecerf@univ-tlse3.fr;


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