Fresh terrestrial detritus fuels both heterotrophic and autotrophic activities in the planktonic food web of a tropical reservoir: a mesocosm study

Abstract

Inland aquatic ecosystems play an important role in the global carbon cycle as they actively mineralize large amounts of terrestrial organic matter. However, there is not much evidence that this allochthonous organic matter affects the energy and matter flow through trophic chain via the microbial food web in tropical reservoirs. We hypothesize that the fresh terrestrial dissolved organic matter (DOM) input in aquatic ecosystems increases net heterotrophy via microbes. A field experiment was conducted in mesocosms, with two treatments: one received detritus input of freshly sampled terrestrial vegetation and the other treatment had no additions (control). The detritus input resulted in increased net heterotrophy and respiration rates after 2 days and increased primary production after 21 days. Moreover, it also changed the zooplankton community to the dominance of copepods, cyclopoids and rotifers, which could have stabilized bacterial abundance and increased bacterial respiration (BR). Our results suggest that fresh terrestrial organic matter input in aquatic systems experiencing wide water level fluctuations (e.g. due to changes in climatic patterns) affect metabolism through two main pathways: (i) initially increasing net heterotrophy via direct DOM bacterial mineralization and planktonic respiration, (ii) later stimulating primary production and net autotrophy due to the nutrients mineralization.