Phytoplankton size-scaling of net-energy flux across light and biomass gradients.

5 years ago

Phytoplankton size-scaling of net-energy flux across light and biomass gradients.

Malerba, Marshall, White

Many studies examine how body size mediates energy use, but few examine how size simultaneously regulates energy acquisition. Furthermore, rarely energy fluxes are examined while accounting for the role of biotic and abiotic factors in which they are nested. These limitations contribute to an incomplete understanding of how size affects the transfer of energy through individuals, populations, and communities. Here we characterized photosynthesis-irradiance (P-I) curves and per-cell net-energy use for 21 phytoplankton species spanning across 4 orders of magnitude of size and 7 phyla, each measured across 6 light intensities and 4 population densities. We then used phylogenetic mixed models to quantify how body size influences the energy turnover rates of a species, and how this changes across environments. Rate-parameters for the P-I curve and net-energy budgets were mostly highly correlated and consistent with an allometric size-scaling exponent of less than 1. The energy flux of a cell decreased with population density and increased with light intensity, but the effect of size remained constant across all combinations of treatment levels (i.e. no size X population density interaction). The negative effect of population density on photosynthesis and respiration is mostly consistent with an active downregulation of metabolic rates following a decrease in per-cell resource availability, possibly as an adaptive strategy to reduce the minimum requirements of a cell and improve its competitive ability. Also, because an increase in body size corresponds to a less-than-proportional increase in net-energy (i.e. exponent<1), we propose that volume-specific net-energy flux can represent an important cost of evolving larger body sizes in autotrophic single-cell organisms. This article is protected by copyright. All rights reserved.

Publisher URL: http://doi.org/10.1002/ecy.2032

DOI: 10.1002/ecy.2032