Hydrological pulse regulating the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes.

Luciana O Vidal,Michaela L Melo,Patrícia Moreira-Turcq,Gwenäel Abril,Marcelo C Bernardes,Fabio Roland,Marc Benedetti,Lúcia M Lobão,Luiz F Artigas,Valdemar L Tornisielo,Mariana C Reis

doi:10.3389/fmicb.2015.01054

Abstract

We evaluated in situ rates of bacterial carbon processing in Amazonian floodplain lakes and mainstems, during both high water (HW) and low water (LW) phases (p < 0.05). Our results showed that bacterial production (BP) was lower and more variable than bacterial respiration, determined as total respiration. Bacterial carbon demand was mostly accounted by BR and presented the same pattern that BR in both water phases. Bacterial growth efficiency (BGE) showed a wide range (0.2–23%) and low mean value of 3 and 6%, (in HW and LW, respectively) suggesting that dissolved organic carbon was mostly allocated to catabolic metabolism. However, BGE was regulated by BP in LW phase. Consequently, changes in BGE showed the same pattern that BP. In addition, the hydrological pulse effects on mainstems and floodplains lakes connectivity were found for BP and BGE in LW. Multiple correlation analyses revealed that indexes of organic matter (OM) quality (chlorophyll-a, N stable isotopes and C/N ratios) were the strongest seasonal drivers of bacterial carbon metabolism. Our work indicated that: (i) the bacterial metabolism was mostly driven by respiration in Amazonian aquatic ecosystems resulting in low BGE in either high or LW phase; (ii) the hydrological pulse regulated the bacterial heterotrophic metabolism between Amazonian mainstems and floodplain lakes mostly driven by OM quality.

Highlights

Bacterioplankton is considered the main agent for the removal of organic carbon (C) in aquatic systems (Williams, 2000)
Our results showed that indexes of organic matter (OM) quality were the strongest seasonal drivers of bacterial carbon metabolism
Our results showed that the hydrologic connectivity, through carbon quality, differentially drives bacterial carbon allocation across freshwater Amazonian ecosystems

Summary

Introduction

Bacterioplankton (generic term including heterotrophic aerobic Bacteria and Archaea) is considered the main agent for the removal of organic carbon (C) in aquatic systems (Williams, 2000). The filtration process can cause: the removal of the pressure by competitors and predators (Martínez-García et al, 2013); structure disruption of bacterial community (Del Giorgio and Cole, 1998; Del Giorgio et al, 2011); phytoplankton cells to suffer rupture; and the release of labile organic C to the filtered (Hopkinson et al, 1989) resulting overestimation of respiration measurements. Bacteria within a water column can reach high abundances in microhabitats such as aggregates (Grossart and Tang, 2010). This aspect is enhanced in Amazonian freshwater ecosystems due to the high levels of suspended materials. Amazonian aquatic ecosystems show high levels of turbidity reaching 151 nephelometric turbidity units (NTU) in mainstems and 128 NTU in floodplains lakes

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