Abstract
The number of species of autotrophic communities can increase ecosystem productivity through species complementarity or through a selection effect which occurs when the biomass of the community approaches the monoculture biomass of the most productive species. Here we explore the effect of resource supply on marine primary productivity under the premise that the high local species richness of phytoplankton communities increases resource use through transient selection of productive species. Using concurrent measurements of phytoplankton community structure, nitrate fluxes into the euphotic zone and productivity from a temperate coastal ecosystem, we find that observed productivities are best described by a population growth model in which the dominant species of the community approach their maximum growth rates. We interpret these results as evidence of species selection in communities containing a vast taxonomic repertory. The prevalence of selection effect was supported by open ocean data that show an increase in community dominance across a gradient of nutrient availability. These results highlight the way marine phytoplankton optimize resources and sustain world food stocks. We suggest that the maintenance of phytoplankton species richness is essential to sustain marine primary productivity since it guarantees the occurrence of highly productive species.
Highlights
Despite half of global primary production being mediated by the activity of microscopic algae called phytoplankton, the effect of phytoplankton species richness on marine primary productivity lacks a mechanistic understanding
The coexistence of species in marine phytoplankton communities depends to a large extent on (i) functional trade-offs among species competing for the same suite of resources (Margalef, 1978; Sommer, 1985; Litchman and Klausmeier, 2008), (ii) chaotic competitive interactions which lead to oscillations in species abundances (Huisman and Weissing, 1999), and (iii) the enormous potential of planktonic microorganisms for dispersal, which repeatedly reshuffles community structure (Finlay, 2002)
Our analysis provides a new insight into the effect of phytoplankton species richness on marine primary productivity beyond the classical two-dimensional species richnessproductivity approach
Summary
Despite half of global primary production being mediated by the activity of microscopic algae called phytoplankton, the effect of phytoplankton species richness on marine primary productivity lacks a mechanistic understanding. The coexistence of species in marine phytoplankton communities depends to a large extent on (i) functional trade-offs among species competing for the same suite of resources (Margalef, 1978; Sommer, 1985; Litchman and Klausmeier, 2008), (ii) chaotic competitive interactions which lead to oscillations in species abundances (Huisman and Weissing, 1999), and (iii) the enormous potential of planktonic microorganisms for dispersal, which repeatedly reshuffles community structure (Finlay, 2002) These features suggest that species complementarity in marine phytoplankton influences primary productivity to a much lesser extent than in terrestrial plant communities
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