Abstract
Ocean-related global change has strongly affected the competition between key marine phytoplankton groups, such as diatoms and dinoflagellates, especially with the deleterious consequency of the increasing occurrence of harmful algal blooms. The dominance of diatoms generally shifts toward that of dinoflagellates in response to increasing temperature and reduced nutrient availability; however, contradictory findings have also been observed in certain sea areas. A key challenge in ecology and biogeochemistry is to quantitatively determine the effects of multiple environmental factors on the diatom-dinoflagellate community and the related changes in elemental and biochemical composition. Here, we test the interplay between temperature, nutrient concentrations and their ratios on marine diatom-dinoflagellate competition and chemical composition using bi-algal competition experiments. The ubiquitous diatom Phaeodactylum tricornutum and dinoflagellate Prorocentrum minimum were cultivated semi-continuously, provided with different N and P concentrations (three different levels) and ratios (10:1, 24:1, and 63:1 molar ratios) under three temperatures (12, 18, and 24°C). The responses of diatom-dinoflagellate competition were analyzed by a Lotka-Volterra model and quantified by generalized linear mixed models (GLMMs) and generalized additive models (GAMs). The changes in nutrient concentrations significantly affected diatom-dinoflagellate competition, causing a competitive superiority of the diatoms at high nutrient concentrations, independent of temperature and N:P supply ratios. Interestingly, the effect amplitude of nutrient concentrations varied with different temperatures, showing a switch back toward a competitive superiority of the dinoflagellates at the highest temperature and at very high nutrient concentrations. The ratios of particulate organic nitrogen to phosphorus showed significant negative correlations with increasing diatoms/dinoflagellates ratios, while lipid biomarkers (fatty acids and sterols) correlated positively with increasing diatoms/dinoflagellates ratios over the entire ranges of temperature, N and P concentrations and N:P ratios. Our results indicate that the integration of phytoplankton community structure and chemical composition provides an important step forward to quantitatively understand and predict how phytoplankton community changes affect ecosystem functions and biogeochemical cycles in the ocean.
Highlights
The changes in hydrological conditions and climate warming have strongly influenced phytoplankton community composition, which affects marine food webs and biogeochemical cycles as different phytoplankton groups have varying contributions to the ocean’s biological pump (Falkowski and Oliver, 2007)
We observed that the interaction coefficient α varied with temperature, showing higher values at the lowest temperature under normal-nutrient conditions, but higher values at higher temperatures under the highest nutrient concentrations (α > 0 indicating the competitive superiority of dinoflagellates; Figure 2)
This study shows that the effect of nutrient concentrations is key in regulating diatom-dinoflagellate competition, as revealed by the competition coefficient, elemental stoichiometry and lipid biomarkers (FAs and sterols)
Summary
The changes in hydrological conditions and climate warming have strongly influenced phytoplankton community composition, which affects marine food webs and biogeochemical cycles as different phytoplankton groups have varying contributions to the ocean’s biological pump (Falkowski and Oliver, 2007). Ocean-related global change has significant effects on the chemical composition of phytoplankton (Guschina and Harwood, 2009; Hixson and Arts, 2016; Ding et al, 2019; Bi et al, 2020), e.g., showing up to a 83% increase in stoichiometric P:C in response to warming and a 76% increase in carbon-normalized contents of polyunsaturated fatty acids (PUFAs) in response to nutrient deficiency (Bi et al, 2017). Despite this increasing awareness of strong variations in the chemical composition of phytoplankton, little is known about the quantitative relationship between marine phytoplankton community structure and its chemical composition in the changing environments
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
