Shifts from nutrient to energy limitation determine the responses of autotrophs, bacteria and mixotrophs to browning

Heterotrophic, mixotrophic, and autotrophic plankton interact in a network of competitive, predatory and mutualistic interactions. “Browning”, the increase of colored dissolved organic matter (CDOM) from terrestrial catchments, can affect this network of interactions by simultaneously decreasing light availability and increasing organic carbon and nutrient supplies. We introduce a conceptual, process-based numerical model to investigate the effects of browning on a microbial food web consisting of heterotrophic bacterioplankton, bacterivorous phago-mixoplankton, autotrophic phytoplankton, and the resources light, inorganic phosphorus, and DOM. We also explore how the investment in autotrophic vs. phagotrophic resource acquisition influences mixoplankton performance. Several model predictions are in broad agreement with empirical observations along a large gradient of increasing CDOM supply, including increased bacterial biomass and inorganic phosphorous, decreased light penetration, the potential for a unimodal phytoplankton biomass response, and a local minimum in mixoplankton biomass. Our results also suggest that mixoplankton with a high investment in phototrophy perform best in many conditions, but that phosphorous acquisition via prey is crucial under high light-low nutrient conditions. Overall, our model analyses suggest that responses to altered CDOM supply are largely determined by systematic changes in the relative importance of nutrient vs. energy limitation of each plankton group.

Presentation Preference: Oral

Primary Presenter: Sebastian Diehl, Umea University (sebastian.diehl@umu.se)

Authors:

Sierra Cagle, Texas A&M University Galveston  (sec1414@tamug.edu)