Competitive dynamics in two species of marine phytoplankton under non-equilibrium conditions

Abstract

Although mathematical models suggest that competition between primary producers in response to dynamical changes in the availability of a limiting nutrient is non-linear, experimental data supporting this basic hypothesis are sparse. Using continuous culture systems with nitrate as a single limiting nutrient, we present results of competition experiments between 2 species of marine phytoplankton, a diatom Thalassiosira pseudonana and a coccolithophore Coccolithus braarudii. These 2 organisms of similar size represent biogeochemically and ecologically distinct functional groups. Consistent with classical resource competition theory, under steady-state nitrate limitation (i.e. continuous flow chemostats), the diatom was outcompeted by the coccolithophore. However, when pulses of nitrate were provided to the chemostats (i.e. non-equilibrium, dynamical conditions) the diatom outcompeted the coccolithophore. The rate of exclusion was a linear function of the frequency of nitrate pulses. These results experimentally demonstrate that dynamical nutrient supply allows co-existence of 2 primary producers competing for a single limiting nutrient and may help us to understand phytoplankton succession in the ocean.

Nitrate Reductase Knockout Uncouples Nitrate Transport from Nitrate Assimilation and Drives Repartitioning of Carbon Flux in a Model Pennate Diatom

“…Our transcriptomic identification of a putative family of vacuolar transporters reinforces data from marine environments that indicate diatoms have high maximum nutrient uptake rates and storage capabilities (i.e., luxury uptake) relative to rates of immediate assimilation (Dortch et al, 1984;Lomas and Glibert, 2000;Villareal et al, 1993). This ecologically advantageous physiological trait of diatoms under nonequilibrium conditions in the marine environment (Cermeño et al, 2011) may rely, in part, on the capacity of vacuolar transporters to respond quickly to elevated NO 3 2 , as we have observed here in the 1-h response by NR-KO14 cells ( Figures 8A and 8B). Additional factors suggest that EG01952 and three other NO 3 2 ClC cohorts, J28245, J46097, and J52412, encode proteins that are involved in transport NO 3 2 into and out of the vacuole: (1) Their expression profiles in both transcriptomes correspond to the need for NO 3 2 to be pumped either into or out of the vacuole.…”

“…Some of the largest fisheries in the world are driven and maintained primarily by diatom-based CO 2 fixation that is fueled by nitrate (NO 3 2 )-rich, upwelling seawater. Their capacity for rapid uptake and storage of NO 3 2 enables higher growth rates and provides them with a competitive advantage over other species during seasonal blooms (Cermeño et al, 2011). Under conditions of elevated NO 3 2 availability, such as in areas of coastal upwelling which occur in temperate oceans and in polar regions, diatoms may take up NO 3 2 in excess of their immediate needs for growth (Clark et al, 2011;Dortch, 1982;Glibert, 1999, 2000;Villareal et al, 1993).…”

Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

“…However, diatoms have been shown to outcompete e.g. coccolithophores in a situation where intermittent nutrient pulses are provided, such as is the case at the shelf break, thanks to their higher maximum nutrient uptake rates and storage capabilities potentially allowing them to sustain higher growth rates for several generations (Litchman et al, 2007;Cermeño et al, 2011).…”

Continental erosion and the Cenozoic rise of marine diatoms

“…Unlike other phytoplankton, diatoms are equipped with large intracellular vacuoles (about 40% of the volume of the cell), which they use for the storage of inorganic nutrients. Despite its simplicity, the presence of this organelle provides diatoms superior competitive abilities in turbulent environments where nutrients episodically enter the euphotic zone (37,38). These environmental conditions became a dominant feature of the Cenozoic oceans in the late Eocene when the spin-up of the circum-Antarctic current and the growth of Antarctic ice sheets amplified the equator to pole heat gradient, and thereby intensified wind-driven ocean upwelling and nutrient supply dynamics (39,40).…”