Interactive effects of light and nutrients on phytoplankton stoichiometry |
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Authors: | Elizabeth M Dickman Michael J Vanni Martin J Horgan |
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Institution: | (1) Department of Zoology, Miami University, Oxford, OH 45056, USA |
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Abstract: | The stoichiometric composition of autotrophs can vary greatly in response to variation in light and nutrient availability,
and can mediate ecological processes such as C sequestration, growth of herbivores, and nutrient cycling. We investigated
light and nutrient effects on phytoplankton stoichiometry, employing five experiments on intact phytoplankton assemblages
from three lakes varying in productivity and species composition. Each experiment employed two nutrient and eight irradiance
levels in a fully factorial design. Light and nutrients interactively affected phytoplankton stoichiometry. Thus, phytoplankton
C:N, C:P, and N:P ratios increased with irradiance, and slopes of the stoichiometric ratio versus irradiance relationships
were steeper with ambient nutrients than with nutrients added. Our results support the light–nutrient hypothesis, which predicts
that phytoplankton C:nutrient ratios are functions of the ratio of available light and nutrients; however, we observed considerable
variation among lakes in the expression of this relationship. Phytoplankton species diversity was positively correlated with
the slopes of the C:N and C:P versus irradiance relationships, suggesting that diverse assemblages may exhibit greater flexibility
in the response of phytoplankton nutrient stoichiometry to light and nutrients. The interactive nature of light and nutrient
effects may render it difficult to generate predictive models of stoichiometric responses to these two factors. Our results
point to the need for future studies that examine stoichiometric responses across a wide range of phytoplankton communities. |
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Keywords: | Carbon:nitrogen:phosphorus ratio Lake Light– nutrient hypothesis Nitrogen Phosphorus |
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