Priming in the microbial landscape: periphytic algal stimulation of litter‐associated microbial decomposers

Abstract

Microbial communities associated with submerged detritus in aquatic ecosystems often comprise a diverse mixture of autotrophic and heterotrophic microbes, including algae, bacteria, protozoa, and fungi. Recent studies have documented increased rates of plant litter mass loss when periphytic algae are present. We conducted laboratory and field experiments to assess potential metabolic interactions between natural autotrophic and heterotrophic microbial communities inhabiting submerged decaying plant litter of Typha angustifolia and Schoenoplectus acutus. In the field, submerged plant litter was either exposed to natural sunlight or placed under experimental canopies that manipulated light availability and growth of periphytic algae. Litter was collected and returned to the laboratory, where algal photosynthesis was manipulated (light/dark incubation), while rates of bacterial and fungal growth and productivity were simultaneously quantified. Bacteria and fungi were rapidly stimulated by exposure to light, thus establishing the potential for algal priming of microbial heterotrophic decay activities. Experimental incubations of decaying litter with 14C- and 13C-bicarbonate established that inorganic C fixed by algal photosynthesis was rapidly transferred to and assimilated by heterotrophic microbial decomposers. Periphytic algal stimulation of microbial heterotrophs, especially fungal decomposers, is an important and largely unrecognized interaction within the detrital microbial landscape, which may transform our current conceptual understanding of microbial secondary production and organic matter decomposition in aquatic ecosystems.

Nutrients and temperature interact to regulate algae and heterotrophic bacteria in an Alaskan poor fen peatland

“…Algae and heterotrophic bacteria grow in close association (Battin et al 2007), and similar responses to nutrients and warming may not have been independent but instead linked to an exchange of resources within the biofilm (Kuehn et al 2014). In a concurrent study, we demonstrated that nutrient enrichment alone had no effect on bacterial growth without the simultaneous addition of a carbon source (K.H.…”

“…Although algae are not likely to contribute substantially to the structural formation of peat (given their labile nature), they may influence the metabolic environment for heterotrophic metabolism by regulating the fate of nutrients and organic matter at the peat surface (Wyatt et al 2012). Algae can do this in several ways, including through the release of exudates (Bertilsson and Jones 2003), which typically consist of simple carbohydrates and amino acids (Wyatt et al 2012) and promote heterotrophic metabolism in the surrounding biofilm (Kuehn et al 2014). Other important functions of algae in wetlands are dependent on species membership, including nitrogen (N) fixation, which is limited to a few groups of heterocyst-forming cyanobacteria (i.e., blue-green algae).…”

The ecology and biogeochemistry of stream biofilms

“…However, evidence for the priming effect in stream biofilms remains equivocal at present. There is suggestive evidence that the presence of algae stimulates bacterial and fungal growth that is associated with leaf litter 72,73 , but no evidence for the priming effect could be found in hyporheic biofilms 74 .…”

“…However, evidence for the priming effect in stream biofilms remains equivocal at present. There is suggestive evidence that the presence of algae stimulates bacterial and fungal growth that is associated with leaf litter 72,73 , but no evidence for the priming effect could be found in hyporheic biofilms 74 .The extensive diversity of bacteria in stream biofilms makes it extremely difficult to establish relationships between bacterial diversity and biofilm function. For example, complementarity among algal species has been shown to increase the uptake of nitrate by stream biofilms 75 but, although it is plausible that this may also occur among bacteria in biofilms, we are not aware of any such study.…”

Functional and Structural Responses of Hyporheic Biofilms to Varying Sources of Dissolved Organic Matter

“…The interaction of these different organic matter pools has potentially important implications for carbon cycling in stream ecosystems (9). For instance, labile organic matter may enhance microbial degradation of recalcitrant organic matter through priming or cometabolism (1,(9)(10)(11). Therefore, knowledge of the structure and functioning of the microbial communities dwelling in the hyporheic zone and their potential response to variations in the DOM supply is important to better assess the role of the hyporheic zone for biogeochemical processes.…”