Abstract
The spatial distribution of bacterioplankton communities in rivers is driven by multiple environmental factors, including local and regional factors. Local environmental condition is associated with effect of river water chemistry (through species sorting); ecological process in region is associated with effects of land use and geography. Here, we investigated variation in bacterioplankton communities (free-living, between 0.22 and 5 μm) in an anthropogenically disturbed river using high-throughput DNA sequencing of community 16S rRNA genes in order to investigate the importance of water chemistry, land use patterns, and geographic distance. Among environmental factors, sulfate (SO42–), manganese (Mn), and iron (Fe) concentrations were the water chemistry parameters that best explained bacterioplankton community variation. In addition, forest and freshwater areas were the land use patterns that best explained bacterioplankton community variation. Furthermore, cumulative dendritic distance was the geographic distance parameter that best explained bacterial community variation. Variation partitioning analysis revealed that water chemistry, land use patterns, and geographic distances strongly shaped bacterioplankton communities. In particular, the direct influence of land use was prominent, which alone contributed to the highest proportion of variation (26.2% in wet season communities and 36.5% in dry season communities). These results suggest that the mechanisms of species sorting and mass effects together control bacterioplankton communities, although mass effects exhibited higher contributions to community variation than species sorting. Given the importance of allochthonous bacteria input from various land use activities (i.e., mass effects), these results provide new insights into the environmental factors and determinant mechanisms that shape riverine ecosystem communities.
Highlights
Bacterioplankton compositions reflect environmental changes in riverine ecosystems due to the sensitivity of their responses to environmental conditions (Marshall et al, 2008)
After subsampling reads to 35,051 reads per sample, a total of 3,945 operational taxonomic units (OTUs) were identified in the communities using a 97% nucleotide sequence identity threshold
OTU numbers, sequence reads, and taxonomic diversity were higher in the dry season communities than wet season communities (Supplementary Table 2)
Summary
Bacterioplankton compositions reflect environmental changes in riverine ecosystems due to the sensitivity of their responses to environmental conditions (Marshall et al, 2008). Changes in river water quality and flow hydraulics/hydrology act together with changes that affect bacterial dispersal and alter spatial patterns of community assembly (Philippe et al, 2020). Numerous studies have indicated that bacterioplankton communities are affected by many environmental factors (Niño-García et al, 2016b; Huang and Huang, 2019; Wang et al, 2019) including water chemistry, land use types, and geographic distances. Interactive effects among the environmental factors that affect bacterial communities remain unclear in these ecosystems Research on these determinant factors has driven focus on the determinant mechanisms (Adams et al, 2014; Niño-García et al, 2016a; Wang et al, 2019)
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