Ecological significance of autotroph–heterotroph microbial interactions in freshwaters

Abstract

Abstract Ecologists often separate pathways of energy flow into those based on either autotrophy (green) or heterotrophy (brown). While these two pathways are easily separated by concept and methodology, increasing evidence shows a complex interplay between autotrophic and heterotrophic components of ecosystems. In freshwater settings, autotroph–heterotroph microbial interactions range widely. Studies suggest that algal–bacterial and algal–fungal interactions can encompass competition, mutualism, and priming effects that depend on environmental factors and can alter ecosystem processes including energy flow and nutrient cycling. Other studies suggest that primary consumers do not feed exclusively in either brown or green food webs, blurring the distinctions between trophic pathways. This omnivory complicates trophic classification, and its nutritional significance is important to understand autotrophy, heterotrophy, and detritus as the basis of consumer growth and fitness. This special issue addresses knowledge gaps regarding the breadth and complexity of the autotroph–heterotroph microbial interface in freshwaters. The nine manuscripts within this special issue showcase the range of topics crossing the boundary between green and brown food webs to understand organism‐ to ecosystem‐level responses to light regime, nutrient availability, temperature, and other environmental factors that affect autotroph–heterotroph interactions. We highlight knowledge gaps generated from this special issue, such as a need for additional field studies documenting autotroph–heterotroph microbial interactions particularly in lentic settings, and a need to scale interactions from the field up to food webs and ecosystems. We anticipate that this special issue will spur scientific interest in both autotrophy and heterotrophy in freshwaters, including how these energy flow pathways cannot be fully understood when studied in isolation.