AME 60:261-272 (2010)  -  DOI: https://doi.org/10.3354/ame01429

ABSTRACT: While microbial aquatic communities are dominated numerically by viruses, both bacterioplankton and phytoplankton play a basal role in the carbon cycle, producing and mineralizing organic matter and driving CO₂ concentrations. Both weak and strong relationships between these 2 microbial groups have been reported for temperate ecosystems. However, data from the tropics and sub-tropics are still scarce, and no consistent pattern regarding the structural microbial connections in these aquatic environments is known so far. We examined bacteria-phytoplankton abundance relationships for tropical freshwaters in comparison to well-studied temperate aquatic ecosystems. We present data on bacterioplankton and phytoplankton abundances in a large data set (1644 samples; lakes, rivers, and reservoirs) from sampling throughout an extensive gradient of latitude (3°N to 33°S) and longitude (35° to 70°W) in tropical waters. We found a generally weak, but significant, relationship between bacterioplankton and phytoplankton abundances and between bacterioplankton and chlorophyll. However, analyzing system by system, we observed an increase in the strength of the relationships (expressed by the determination coefficient, r²), from 0.05 to 0.17 (bacterioplankton and phytoplankton abundances) and from 0.09 to 0.44 (bacterial abundance and chl a). Our data suggest that the in-system ecological drivers (e.g. water temperature, trophic state, and flushing characteristics, i.e. lentic or lotic) determine the bacterioplankton abundance patterns more than other factors such as latitude or system typology. In a global perspective, the comparison between non-tropical and tropical/sub-tropical freshwaters showed that a lower proportion of phytoplankton carbon is transformed into bacterial carbon in the tropics.

KEY WORDS: Microbial dynamics · Bacterial–phytoplankton coupling · Tropical waters