Body size, light intensity, and nutrient supply determine plankton stoichiometry in mixotrophic plankton food webs
Journal
American Naturalist
Journal Volume
195
Journal Issue
4
Start Page
E100
End Page
E111
ISSN
0003-0147
1537-5323
Date Issued
2020-04-01
Author(s)
DOI
10.1086/707394
Abstract
Trophic strategy determines stoichiometry of plankton. In general, heterotrophic zooplankton have lower and more stable C:N and C:P ratios than photoautotrophic phytoplankton, whereas mixotrophic protists, which consume prey and photosynthesize, have stoichiometry between zooplankton and phytoplankton. As trophic strategies change with cell size, body size may be a key trait influencing eukaryotic plankton stoichiometry. However, the relationship between body size and stoichiometry remains unclear. Here we measured plankton size-fractionated C:N ratios under different intensities of light and nutrient supply in subtropical freshwater and marine systems. We found a unimodal body size–C:N ratio pattern, with a maximum C:N ratio at ~50 mm diameter in marine and freshwater systems. Moreover, the variation in C:N ratios is explained mainly by body size, followed by light intensity and nutrient concentration. To investigate the mechanisms behind this unimodal pattern, we constructed a size-based plankton food web model in which the trophic strategy and C:N ratio are an emerging result. Our model simulations reproduce the unimodal pattern with a C:N ratio of photoautotrophs ≤50 mm increasing with body size due to increase of photosynthetic carbon, whereas C:N ratios of organisms >150 μm decrease with size due to decreasing photoautotrophic but increasing heterotrophic uptake. Based on our field observations and simulation, we extend the classic “light-nutrient” theory that determines plankton C:N ratio to include body size and trophic strategy dependency. We conclude that body size and size-dependent uptake of resources (light, nutrients, and prey) determine plankton stoichiometry at various light and nutrient supplies.
Subjects
Ecological stoichiometry
Mixotrophy
Size-based resource affinity
Trophic strategy
Publisher
University of Chicago Press
Type
journal article