SFS Annual Meeting

5/21/2018  |   09:00 - 09:15   |  321

NAVIGATING THE BOUNDARY BETWEEN GREEN AND BROWN: WHERE, WHEN, AND HOW DO AUTOTROPH-HETEROTROPH INTERACTIONS AFFECT AQUATIC SYSTEMS? Many approaches in ecosystem ecology focus on separate pathways of energy flow based on either autotrophy or heterotrophy (“green” or “brown” systems, respectively). While these two pathways are easily separated by concept and methodology, recent research from freshwaters suggests autotrophy and heterotrophy often occur in close proximity and interact in complex ways. Studies investigating algal-bacterial and algal-fungal interactions, for example, point to a range of possible interactions including competition, mutualism, and priming effects that depend on environmental factors and can alter organic matter processing. Further blurring distinctions between trophic pathways, studies increasingly suggest primary consumers do not feed exclusively in either brown or green food webs. This omnivory complicates trophic classification, and its nutritional significance is important to understand autotrophic, heterotrophic, and non-living organic matter as the basis of consumer growth and fitness. In this presentation, we introduce topics crossing the boundary between green and brown to understand organism- to ecosystem-level responses to light regime, nutrient availability, temperature, and other factors that affect autotroph-heterotroph interactions. We and fellow special session presenters will highlight current knowledge and provide direction for future inquiry at this important yet complex interface in aquatic systems.

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


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


Caleb J. Robbins (Co-Presenter/Co-Author), University of Alaska Fairbanks, Caleb_Robbins@baylor.edu;


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5/21/2018  |   09:15 - 09:30   |  321

META-ANALYSIS OF HETEROTROPHIC MICROBIAL RESPONSES TO PERIPHYTIC ALGAL PHOTOSYNTHESIS Numerous studies have investigated heterotrophic microbial responses to algal photosynthesis. Here we report the results of a meta-analytical synthesis of published and unpublished experiments (N ranging from 8 to 46) focused on the responses of heterotrophic microbial production (bacterial and fungal) and extracellular enzyme activity (beta-glucosidae, beta-xylosidase, leucine aminopeptidase, phosphatase, and phenol oxidase) to concurrent algal photosynthesis in periphyton communities. Algal photosynthesis caused significantly increased activity in all response variables, except for beta-xylosidase and phenol oxidase where the trends were positive, but not statistically significant. Fungal production was stimulated by photosynthesis to a significantly greater degree than any other heterotrophic response, suggesting that fungal-algal interactions may be of particular importance in periphyton communities.

Steve Francoeur (Primary Presenter/Author), Biology Department, Eastern Michigan University, steve.francoeur@emich.edu;


Halvor Halvorson (Co-Presenter/Co-Author), University of Central Arkansas, hhalvorson@uca.edu;


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


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5/21/2018  |   09:30 - 09:45   |  321

SIMULATING INTERACTIVE EFFECTS OF PRIMARY PRODUCTION AND TERRESTRIAL ORGANIC MATTER SUBSIDIES ON STREAM ORGANIC CARBON SPIRALING Despite recent advances in our understanding of inland waters as active players in the carbon cycle, most studies have not addressed the mechanisms behind larger-scale patterns. Consequently, quantifying how organic carbon (OC) is mineralized in streams and rivers is a necessary step toward a broader knowledge of the mechanisms controlling OC fluxes and fate. Here we link experimental data and model simulations to infer how non-additive interactions between algal- and terrestrially-derived OC (e.g., a priming effect) can alter stream OC spiraling. We ask: how do different organic matter compounds exported to and produced within streams/rivers interact to alter net OC transformations? Non-additive effects of mixed carbon sources on stream OC transformations can influence whole-ecosystem OC tracer uptake measurements, but are difficult to separate from OC metabolism and spiraling without single-source experiments and multi-source models. In recognition that many studies have failed to find conclusive evidence of a priming effect in freshwater ecosystems, we further explore a range of simulation scenarios to discuss the magnitude of non-additive responses needed to identify priming of OC transformations given rapid OC mineralization and high variation common to bioassay and in-stream solute dynamics.

Erin R. Hotchkiss (), Virginia Tech, ehotchkiss@vt.edu;


Erin Hotchkiss (Primary Presenter/Author), Virginia Polytechnic Institute and State University (Virginia Tech), ehotchkiss@vt.edu;


Robert O. Hall (Co-Presenter/Co-Author), Flathead Lake Biological Station, University of Montana, bob.hall@flbs.umt.edu;


Michelle Baker (Co-Presenter/Co-Author), Utah State University, michelle.baker@usu.edu;


Stephen Plont (Co-Presenter/Co-Author), Virginia Tech, plontste@vt.edu;


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5/21/2018  |   09:45 - 10:00   |  321

LITTER NUTRIENT CONTENT MEDIATES THE EFFECTS OF PERIPHYTIC ALGAL PHOTOSYNTHESIS ON FUNGAL AND BACTERIAL PRODUCTION IN LITTER-ASSOCIATED MICROBIAL COMMUNITIES Studies have documented metabolic couplings between autotrophic and heterotrophic microbial communities inhabiting plant litter, establishing the potential for algal stimulation or “priming” of microbial decomposers. Despite this evidence, the importance and magnitude of algal stimulation of microbial heterotrophs remain poorly understood in relation to detrital nutrient quality. We examined photosynthetically-mediated interactions among microbes inhabiting nutrient (N & P) enriched and unenriched litter of Schoenoplectus acutus and Typha angustifolia. We grew natural periphyton communities (algae, bacteria, and fungi) on submerged Schoenoplectus and Typha litter, and then manipulated photosynthesis using the photosystem II inhibitor DCMU while simultaneously quantifying rates of algal, bacterial and fungal productivity. DCMU prevented algal photosynthesis (p ? 0.01) on plant litter. Furthermore, active photosynthesis stimulated both fungal (p ? 0.01) and bacterial (p ? 0.05) productivity. The magnitude of algal stimulatory effects on fungal production were higher in unenriched litter and were significantly related to litter C:N and C:P ratios (p ? 0.05). This study reveals that periphytic algae directly influence heterotrophic microbial decomposers and that the strength of algal stimulatory effects may decrease under detrital nutrient enrichment.

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


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


Steve Francoeur (Co-Presenter/Co-Author), Biology Department, Eastern Michigan University, steve.francoeur@emich.edu;


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5/21/2018  |   10:00 - 10:15   |  321

THE ROLE OF PHOSPHORUS AND LIGHT IN AQUATIC MICROBIAL PRIMING The aquatic priming effect (PE) hypothesis states recalcitrant organic matter (ROM) has increased decomposition in low-nutrient environments when labile organic matter (LOM), (e.g. dissolved organic carbon (DOC)), is added. Likewise, ROM decomposition decreases with increases in available nutrients and C. Anthropogenic activities can alter the amount of nutrients and light reaching headwaters, where these inputs are usually limited, potentially altering OM decomposition via microbial priming. This has important implications in how humans influence large-scale C and nutrient flux. We performed a recirculating stream mesocosm experiment manipulating phosphorus (P) and light to investigate how autotrophic and heterotrophic microbes would be affected and interact to affect ROM decomposition. Light-time and light-P interactions drove increases in suspended (p=0.001) and detrital (p=0.0036) algal biomass, respectively. Light-time interaction drove increased DOC (p=0.029). Time and P (p=<0.001; 0.008, respectively) drove increased heterotrophic biomass. These results agree with other studies showing increases in algal biomass resulted in elevated DOC inputs that may have stimulatory effects on heterotrophic microbes, especially in low-nutrient environments. We calculated PE as an effect size (ambient-shade treatments) within P concentrations for ROM. Our results indicate light and nutrients may mediate aquatic microbial priming.

Brooke Howard-Parker (Primary Presenter/Author), University of Arkansas, bbhowardparker@gmail.com;


Brendon White (Co-Presenter/Co-Author), University of Arkansas, blw023@email.uark.edu;


Michelle Evans-White (Co-Presenter/Co-Author), University of Arkansas, mevanswh@uark.edu;


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5/21/2018  |   10:15 - 10:30   |  321

EXPERIMENTAL EVIDENCE SUGGESTS ALGAE NEGATIVELY PRIME PLANT LITTER DECOMPOSITION IN AQUATIC SYSTEMS During plant litter decomposition, periphytic algae provide fresh, labile carbon that may stimulate decomposer microbes and enhance decomposition of underlying recalcitrant litter through positive priming effects (PEs). Despite their potential importance, the direction and magnitude of algal PEs in aquatic settings remain poorly tested. We synthesize two experimental tests of algal PE during decomposition of cattail litter (lentic system) and water oak and tulip poplar litter (lotic system) using extended light versus dark manipulations. In both experiments, light permitted algal growth, which in turn stimulated fungal production rates (P<0.001) but, compared to dark-incubated litter, reduced fungal biomass (P<0.001) and litter mass loss rates (P<0.001). While effects of light on bacteria were comparatively weaker, light also reduced phenol oxidase and beta glucosidase activities in the lentic system, suggesting algae inhibited degradative enzyme activity on litter. These findings are indicative of negative PE, in which labile algal-derived carbon stimulates decomposers, but perhaps due to preferential substrate use, decomposers do not increase degradation of recalcitrant litter as expected under positive PE. Drawn from separate systems, our similar findings suggest increased light availability could suppress microbial decomposition of organic matter in many freshwater settings.

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


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


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


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


Jacob Barry (Co-Presenter/Co-Author), University of Southern Mississippi, jacobbarry88@gmail.com;


Matthew Lodato (Co-Presenter/Co-Author), University of Alabama, mlodato@crimson.ua.edu;


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