Solar radiation-nutrient interaction enhances the resource and predation algal control on bacterioplankton: A short-term experimental study

Abstract

An in situ experimental assessment was made of the effects of the interaction between spectral composition of solar radiation and the limiting nutrient (phosphorous, P) on the algae-bacteria link, measured over the short term (1.5 h after P enrichment) in an oligotrophic and autotrophic high mountain lake. Variables related to the metabolism of algae (primary production, excretion of photosynthetic carbon) and bacteria (bacterial production, percentages of photosynthetic exudates assimilated and used for bacterial production) were studied. P enrichment suppressed or attenuated the negative effects exerted by ultraviolet radiation on algae when their elemental composition was P deficient. This was reflected in antagonistic interactive effects between P enrichment and solar radiation (P × R), which were triggered by a decrease in primary production and an increase in organic carbon excretion due to metabolic adjustments to growth. P enrichment also suppressed or attenuated the main effects exerted by ultraviolet radiation on bacteria. This was reflected in antagonistic P ×R interactive effects triggered by an enhancement of the dual control (resource and predation) that algae exerted on bacteria and by the growth stimulation of P-deficient bacteria after P enrichment. All of these observed responses contribute to improving the food quality for herbivores and reinforce the flux of carbon and nutrient to the grazing chain, which explains its development in this and other clear-water ecosystems.