Marine bacterioplankton communities respond to cadmium (Cd) stress in microcosms over time

Temporal variability of bacterioplankton community has been considered as ubiquitous process in marine aquatic ecosystems. However, far less is known about the temporal dynamics of bacterioplankton community responding to anthropogenic disturbances such as heavy metal pollution. In this study, we used replicated seawater-containing microcosms perturbed with 0, 10, 100, and 1000 ????g L-1 of cadmium (Cd, as a reprehensive heavy metal) for two weeks to investigate temporal variability, Cd-induced patterns, and their interaction in bacterial community and to find out whether the bacterial community structures would indicate Cd pollution intensity in temporal varying system. Our results showed that elevated Cd levels consistently shifted marine bacterial community structure after 4-d incubation. However, the community exhibited some resistance to Cd at slight level (10 ????g L-1). Arm race between temporal variability and Cd stress was observed, and the temporal variability overwhelmed Cd-induced patterns in bacterial community. Temporal succession of bacterial community were correlated with pH, dissolved oxygen, NO3--N, NO2--N, PO43--P, dissolved organic carbon, and chlorophyll a, and each of these parameters contribute more to community variance than Cd did. However, elevated Cd levels did decrease the turnover rate of temporal succession of community. Furthermore, potential Cd indicator taxa almost affiliated with Bacteroidetes, Alphaproteobacteria, and Gammaproteobacteria were identified, and these taxa showed highly frequent occurrence during two weeks. This study provides direct evidence that specific Cd-induced patterns to bacteriolankton community exist in marine ecosystem with high temporal variability and further demonstrated the importance of determining indicator taxa on temporal scales.