Bacterial growth efficiency: Do consumer and resource diversity influence the fate of carbon in aquatic ecosystems?
Bacterial growth efficiency (BGE) has major implications for ecosystem function and trophic dynamics. In aquatic ecosystems BGE influences the relative contribution of resources towards greenhouse gas emissions and food web biomass. It is well established that environmental factors such as nutrient concentrations and temperature have a strong influence on consumer physiology. However, these environmental factors are not sufficient to explain the observed variation in BGE. We hypothesize that consumer and resource diversity are important drivers of BGE. Furthermore, we predict that phylogenetic relationships between consumers will constrain observed variation. In this study, we quantified BGE on 30 aquatic isolates representing five major clades of bacteria. We measured BGE using a suite of carbon resources typical in the breakdown of terrestrial carbon in aquatic ecosystems.
Our results showed that there are significant differences in BGE based on consumer and resource diversity. In addition, we detected a strong phylogenetic signal of these resource allocation traits across our study organisms. Specifically, we found that some of the more complex resources (e.g., protocatechuate) were constrained to specific lineages of bacteria. These results suggest that physiological traits related to BGE are evolutionarily constrained and thus community composition could explain variation in BGE. For example, given the diversity of resources in an environment, the presence of specialized bacterial lineages could have a strong influence on bulk BGE. As such, the results of this study have implications for understanding how bacterial community diversity influences ecosystem function and trophic dynamics across aquatic habitats.