Modeling silicate–nitrate–ammonium co-limitation of algal growth and the importance of bacterial remineralization based on an experimental Arctic coastal spring bloom culture study

Abstract

Abstract. Arctic coastal ecosystems are rapidly changing due to climate warming. This makes modeling their productivity crucially important to better understand future changes. System primary production in these systems is highest during the pronounced spring bloom, typically dominated by diatoms. Eventually the spring blooms terminate due to silicon or nitrogen limitation. Bacteria can play an important role for extending bloom duration and total CO2 fixation through ammonium regeneration. Current ecosystem models often simplify the effects of nutrient co-limitations on algal physiology and cellular ratios and simplify nutrient regeneration. These simplifications may lead to underestimations of primary production. Detailed biochemistry- and cell-based models can represent these dynamics but are difficult to tune in the environment. We performed a cultivation experiment that showed typical spring bloom dynamics, such as extended algal growth via bacterial ammonium remineralization, reduced algal growth and inhibited chlorophyll synthesis under silicate limitation, and gradually reduced nitrogen assimilation and chlorophyll synthesis under nitrogen limitation. We developed a simplified dynamic model to represent these processes. Overall, model complexity in terms of the number of parameters is comparable to the phytoplankton growth and nutrient biogeochemistry formulations in common ecosystem models used in the Arctic while improving the representation of nutrient-co-limitation-related processes. Such model enhancements that now incorporate increased nutrient inputs and higher mineralization rates in a warmer climate will improve future predictions in this vulnerable system.

Tracing basal resource use across sea‐ice, pelagic, and benthic habitats in the early Arctic spring food web with essential amino acid carbon isotopes

“…The bacterial species used in this study were isolated from Arctic sea‐ice algae or phytoplankton enrichments, which indicates that they could be a food source for Arctic sponges. The collected bacteria P. elyakovii can cause aggregate formation in the diatom Chaeotoceros socialis and increase their contribution to the benthic ecosystem (Rapp et al 2018; Vonnahme et al 2021). As the sponge tissue represents an overall inseparable collection of undigested food items, microbiome and indigenous sponge tissue, microbial basal resources used by the sponge might be identified as those not part of the core microbiome.…”

“…Two other bacterial strains, Pseudoalteromonas arctica and Pseudoalteromonas elyakovii were isolated from phytoplankton net hauls that were dominated by the diatom Chaetoceros socialis (0–30 m with a 20 μ m mesh size phytoplankton net) in Kaldfjorden, Tromsø. A detailed description of bacterial strain isolation and identification is described by Vonnahme et al (2021).…”