The effect of temperature increase on microbial carbon fluxes in the Adriatic Sea: an experimental approach

Abstract

An assessment of the temperature increase effect on processes within the microbial food web provides a better insight into the carbon transfer and energy flow processes in marine environments in the global warming perspective. Modified laboratory dilution experiments that allow simultaneous estimates of protozoan grazing and viral lysis on picoplankton groups (bacteria, Prochlorococcus, Synechococcus and pico-eukaryotic algae) under in situ and 3°C above in situ temperatures were performed at seasonal scale. Picoplankton mortality due to grazing was generally higher than that caused by viral lysis, especially in the cold months. The largest part of HNF carbon demand was satisfied by grazing on bacteria throughout the year. Although ciliates satisfied their carbon demand predominantly through grazing on HNF and bacteria, the role of autotrophic picoplankton (APP) as their prey increased significantly in the cold months. Bacteria constituted the most important host for viruses throughout the year. However, during the warm months, APP groups were also significant hosts for viral infection. Under the warming condition the amount of picoplankton biomass transferred to protozoan grazers exceeded the lysed biomass, suggesting that global warming could further increase picoplankton carbon flow toward higher trophic levels in the Adriatic Sea.

Temperature and phosphorus interacts in controlling the picoplankton carbon flux in the Adriatic Sea: an experimental versus field study

“…While the autotrophic picoplankton flux towards predators (both HNF and CIL) increased under all experimental conditions and in all months, the bacterial biomass flux towards HNF in July (maximal HNF grazing on bacteria) and towards CIL in January increased considerably, mainly because of temperature increase. These results confirmed earlier studies in the Adriatic Sea that reported maximal contribution of ciliates to total grazing on bacteria during the winter, while during the warmer period HNF were almost completely responsible for bacterial grazing (Šoli c and Krstulovi c, 1994;Šoli c et al, 2018a). Our study showed that the efficiency of direct carbon transfer from bacteria to ciliates was inversely proportional to the amount of carbon transferred.…”

“…A recent study carried out in the Adriatic Sea also showed a positive response of autotrophic picoplankton abundance to temperature (Šolić et al, , ). This is in accordance with the idea that planktonic autotrophs and heterotrophs are characterized by different activation energies (Chen and Laws, ).…”

“…It should be noted that measured grazing actually included viral lysis, which was not measured in these experiments. A previous study in the Adriatic Sea showed that a rise in temperature also increased the amount of picoplankton biomass lysed by viruses, particularly in warm months (Šolić et al, )…”

“…Besides, bacterial respiration (BR) showed higher relative increase compared to BP under warming conditions (lower bacterial growth efficiency). Reduced BP can further limit bacterial growth in comparison to pico‐autotrophs, especially in the P‐enriched environmental conditions (Šolić et al, ).…”

“…Edwards and Richardson, 2004;Wiltshire et al, 2008;Montoya and Raffaelli, 2010). It is well established that temperature significantly influences microbiological processes such as production (Rivkin et al, 1996;Hoppe et al, 2008;Šoli c et al, 2018a), growth rate (White et al, 1991;Shiah and Ducklow, 1994) and growth efficiency (Rivkin and Legendre, 2001), as well as grazing on bacteria (Vaqué et al, 1994;Krstulovi c, 1994, 1995;Vázquez-Dominguez et al, 2012) and viral lysis (Danovaro et al, 2011;Lara et al, 2013;Maranger et al, 2015;Tsai et al, 2015;Ordulj et al, 2017). Furthermore, temperature influences the complex microbial trophic interactions, altering food web structure and ecosystem functioning (Petchey et al, 1999).…”