Predictable ecological response to rising CO₂ of a community of marine phytoplankton

Abstract

Rising atmospheric CO 2 and ocean acidification are fundamentally altering conditions for life of all marine organisms, including phytoplankton. Differences in CO 2 related physiology between major phytoplankton taxa lead to differences in their ability to take up and utilize CO 2. These differences may cause predictable shifts in the composition of marine phytoplankton communities in response to rising atmospheric CO 2. We report an experiment in which seven species of marine phytoplankton, belonging to four major taxonomic groups (cyanobacteria, chlorophytes, diatoms, and coccolithophores), were grown at both ambient (500 μatm) and future (1,000 μatm) CO 2 levels. These phytoplankton were grown as individual species, as cultures of pairs of species and as a community assemblage of all seven species in two culture regimes (high‐nitrogen batch cultures and lower‐nitrogen semicontinuous cultures, although not under nitrogen limitation). All phytoplankton species tested in this study increased their growth rates under elevated CO 2 independent of the culture regime. We also find that, despite species‐specific variation in growth response to high CO 2, the identity of major taxonomic groups provides a good prediction of changes in population growth and competitive ability under high CO 2. The CO 2‐induced growth response is a good predictor of CO 2‐induced changes in competition (R 2 > .93) and community composition (R 2 > .73). This study suggests that it may be possible to infer how marine phytoplankton communities respond to rising CO 2 levels from the knowledge of the physiology of major taxonomic groups, but that these predictions may require further characterization of these traits across a diversity of growth conditions. These findings must be validated in the context of limitation by other nutrients. Also, in natural communities of phytoplankton, numerous other factors that may all respond to changes in CO2, including nitrogen fixation, grazing, and variation in the limiting resource will likely complicate this prediction.

Quality–quantity trade‐offs drive functional trait evolution in a model microalgal ‘climate change winner’

“…by comparing the Amb populations growing in ambient pCO 2 (pink, left‐hand boxes of each plot) with the Amb populations growing in high pCO 2 (green, middle boxes of each plot). As expected, population growth rate and gross photosynthesis rates increase in the enriched environment in agreement with other studies on this and other microbial systems in marine and freshwater systems (Collins & Bell, ; Dutkiewicz, ; Pardew et al, ; Schaum et al, ) (effect of pCO 2 on population growth rate t 54 = 8.18, P < 0.0001 and gross photosynthesis rate per cell t 54 = 9.54, P < 0.0001). Plastic responses in respiration also occur in most genotypes, though the direction of response varies between genotypes.…”

“…Microbial primary producers (phytoplankton) form the base of aquatic food webs and fix approximately 40% of global carbon annually (Falkowski, ). Photosynthetic microbes respond to increases in carbon dioxide using plastic responses (short‐term change in phenotype with no underlying change in genotype) (Dutkiewicz, ; Pardew et al, ) and evolutionary responses (change in the genetic composition of a population over time) (Boyd, ; Collins et al, ). Phytoplankton can be grouped based on their roles in biogeochemical cycles (calcifyers, silicifyers, nitrogen fixers, other green), and there is variation in both plastic and evolutionary responses to increased CO 2 availability within and between phytoplankton functional groups (Collins et al, ; Dutkiewicz, ; Pardew et al, ; Schaum et al, ).…”

“…Photosynthetic microbes respond to increases in carbon dioxide using plastic responses (short‐term change in phenotype with no underlying change in genotype) (Dutkiewicz, ; Pardew et al, ) and evolutionary responses (change in the genetic composition of a population over time) (Boyd, ; Collins et al, ). Phytoplankton can be grouped based on their roles in biogeochemical cycles (calcifyers, silicifyers, nitrogen fixers, other green), and there is variation in both plastic and evolutionary responses to increased CO 2 availability within and between phytoplankton functional groups (Collins et al, ; Dutkiewicz, ; Pardew et al, ; Schaum et al, ). This variation has led to the prediction that taxa that can respond to nutrient enrichment (such as increased carbon availability) by increasing their population growth rate will increase in frequency as these conditions persist (Dutkiewicz, ; Follows et al, ).…”

Company matters: The presence of other genotypes alters traits and intraspecific selection in an Arctic diatom under climate change

“…When questions are focused on understanding how species within a community may interact by using such setups, monoculture responses seem to predict the community outcomes fairly well (Low-Décarie, Fussmann, & Bell, 2011;Pardew, Pimentel, & Low-Decarie, 2018). Thus far, knowledge about such interactions in phytoplankton mainly stems from research on different species in artificial assemblages, which are typically composed of very few long-term established laboratory strains as representatives of each selected species.…”

“…Thus far, knowledge about such interactions in phytoplankton mainly stems from research on different species in artificial assemblages, which are typically composed of very few long-term established laboratory strains as representatives of each selected species. When questions are focused on understanding how species within a community may interact by using such setups, monoculture responses seem to predict the community outcomes fairly well (Low-Décarie, Fussmann, & Bell, 2011;Pardew, Pimentel, & Low-Decarie, 2018). However, from early agricultural research, we know, that a mix of species can have a different, often even higher yield than the best performing species grown in monoculture ("transgressive overyielding";Trenbath, 1974).…”