Balance between primary and bacterial production in North Patagonian shallow lakes

The shallow Andean North Patagonian lakes are suitable environments for the evaluation of autotrophic and heterotrophic production under a scenario of high radiation in high dissolved organic matter (DOM) systems. We aimed to study the balance between primary and bacterial production in three shallow Andean lakes, in a summer sampling (high irradiance condition). Our hypothesis is that two factors would interact: high light and high DOM, affecting bacteria and algae. We carried out experiments of bacterial production (BP) by measuring [¹⁴C]-l-leucine incorporation and PP by ¹⁴C uptake in two fractions: picophytoplankton and phytoplankton >2 μm. Cell abundance, chlorophyll a, nutrients, DOM, light, and temperature were also measured. The contribution of picophytoplankton to total primary production (PP) was, in general, very high exceeding 50%. Picophytoplankton was photosynthetically more efficient than the larger autotrophs in all lakes. We observed a decrease in PP at surface levels due the high solar irradiances, while BP was not affected. Changes in the PP:BP ratios were observed in relation to DOM content and light effect. Our data indicate that the amount of available DOM drives the balance between PP and BP. However, solar radiation should be included as an important factor since PP:BP ratio may decrease because of PP photoinhibition.