Effects of increasing atmospheric CO2 on the marine phytoplankton and bacterial metabolism during a bloom: A coastal mesocosm study

Abstract

Increases of atmospheric CO concentrations due to human activity and associated effects on aquatic ecosystems are recognized as an environmental issue at a global scale. Growing attention is being paid to CO enrichment effects under multiple stresses or fluctuating environmental conditions in order to extrapolate from laboratory-scale experiments to natural systems. We carried out a mesocosm experiment in coastal water with an assemblage of three model phytoplankton species and their associated bacteria under the influence of elevated CO concentrations. Net community production and the metabolic characteristics of the phytoplankton and bacteria were monitored to elucidate how these organisms responded to CO enrichment during the course of the algal bloom. We found that CO enrichment (1000μatm) significantly enhanced gross primary production and the ratio of photosynthesis to chlorophyll a by approximately 38% and 39%, respectively, during the early stationary phase of the algal bloom. Although there were few effects on bulk bacterial production, a significant decrease of bulk bacterial respiration (up to 31%) at elevated CO resulted in an increase of bacterial growth efficiency. The implication is that an elevation of CO concentrations leads to a reduction of bacterial carbon demand and enhances carbon transfer efficiency through the microbial loop, with a greater proportion of fixed carbon being allocated to bacterial biomass and less being lost as CO. The contemporaneous responses of phytoplankton and bacterial metabolism to CO enrichment increased net community production by about 45%, an increase that would have profound implications for the carbon cycle in coastal marine ecosystems.

Effects of Ocean Acidification on Marine Photosynthetic Organisms Under the Concurrent Influences of Warming, UV Radiation, and Deoxygenation

“…On the other hand, under nutrient replete conditions, growth of diatoms tends to be enhanced (Wu et al, 2014). In coastal eutrophic water, increased partial pressure of CO 2 increased primary production of phytoplankton assemblages dominated by diatoms in a mesocosm study (Huang et al, 2018).…”

Potential overestimation of community respiration in the western Pacific boundary ocean: What causes the putative net heterotrophy in oligotrophic systems?

“…The planktonic community metabolic rates were estimated from the changes in dissolved oxygen concentrations in the light–dark bottles over a 24‐h incubation period following the procedure of Serret et al (). The dissolved oxygen concentrations were determined by high‐precision Winkler titration (Oudot et al ; Huang et al ) with an automated potentiometric end‐point detection system (Metrohm‐848, Switzerland). For each depth, the water samples were carefully siphoned into 12 calibrated 100 mL borosilicate bottles using silicon tubing, with more than 300 mL overflowing.…”

Effect of elevated <i>p</i>CO<sub>2</sub> on trace gas production during an ocean acidification mesocosm experiment

“…Taken together, we inferred that the elevated pCO 2 first delayed growth of DMSP-consuming bacteria; then the delayed DMSP-consuming bacteria postponed the DMSP degradation process, and eventually delayed the DMS concentration in the high pCO 2 treatment. In addition, considering that algae and bacteria in natural seawater were removed through a filtering process before the experiment (Huang et al, 2018), we further concluded that the elevated pCO 2 controlled DMS concentrations mainly by affecting DMSP-consuming bacteria attached to T. weissflogii and P. tricornuntum.…”