Circumpolar synchrony in big river bacterioplankton

Abstract

Natural bacterial communities are extremely diverse and highly dynamic, but evidence is mounting that the compositions of these communities follow predictable temporal patterns. We investigated these patterns with a 3-year, circumpolar study of bacterioplankton communities in the six largest rivers of the pan-arctic watershed (Ob', Yenisey, Lena, Kolyma, Yukon, and Mackenzie), five of which are among Earth's 25 largest rivers. Communities in the six rivers shifted synchronously over time, correlating with seasonal shifts in hydrology and biogeochemistry and clustering into three groups: winter/spring, spring freshet, and summer/fall. This synchrony indicates that hemisphere-scale variation in seasonal climate sets the pace of variation in microbial diversity. Moreover, these seasonal communities reassembled each year in all six rivers, suggesting a long-term, predictable succession in the composition of big river bacterioplankton communities.

Fig. 1.

Watershed map of the six largest rivers in the pan-arctic watershed with red dots indicating sampling sites.

Fig. 2.

Multidimensional scaling diagrams showing synchronous seasonal variation and annual reassembly in bacterioplankton community composition over three years. A calendar bar at the top shows sampling periods. Circled clusters of samples contained similar bacterial communities within each river (ANOSIM R >0.8, P < 0.05). Closed symbols represent samples collected in 2004, open symbols 2005, and symbols with black fill 2003.

Fig. 3.

Map of the 114 major watersheds of the world (35) with marks indicating rivers (red) and lakes (blue) where members of some of the nine dominant OTUs in Table 2 have been found. [Adapted with permission from ref. (Copyright 1998, World Resources Institute).]