Microbial loop processes shape the food web stoichiometry in Lake Kinneret

Nutrient cycling in the pelagic zone of aquatic ecosystems is generally controlled by the interactions between zooplankton, phytoplankton and bacteria. However, very little is known about how microbial interactions influence the stoichiometry of trophic levels within freshwater ecosystems. In order to better understand these interactions, we examined how the microbial loop shaped the N:P stoichiometry of food web components in Lake Kinneret. We used two microbial loop sub-models incorporated into a one-dimensional coupled hydrodynamic-ecological model (DYRESM-CAEDYM) to simulate the effect of microbial loop processes on the N: P stoichiometry of the food web. The stoichiometry of nutrient recycling pathways illustrated that the ability of bacteria to regulate phytoplankton stoichiometry is a significant factor that has ecosystem wide implications. The results showed that the average internal N: P ratios of the combined phytoplankton community followed their C biomass patterns. However, variations in the internal N: P ratios of the five simulated phytoplankton species occurred depending on the operation of the microbial loop, suggesting that predicting the N: P ratios of the nutrient flux pathways between bacteria, zooplankton and inorganic matter are important in correctly predicting the available nutrients for individual phytoplankton groups, and their overall patterns of growth. The dynamic shifts in nutrient stoichiometry induced by changes in the microbial loop within Lake Kinneret provide an improved mechanistic understanding of microbial interactions in aquatic ecosystems.