Although dispersal is known to influence bacterial abundance, diversity, and composition, we know little about the rates and routes by which bacteria disperse into new communities. We hypothesized that, in a grassland, bacteria disperse into the top layer of soil from three main routes – up from soil, horizontally among local vegetation, or down from rain and air – and that these routes differ in their rate of dispersal and taxonomic composition. We manipulated these dispersal routes in a grassland over six months by using litter bags made of 0.22-micron nylon (closed to dispersal) and/or 2 mm window screen (open to dispersal). We quantified the rate and composition of immigrating bacteria on sterile microscope slides. We simultaneously manipulated dispersal into fresh leaf litter to assess impacts on community assembly (16S rDNA) and functioning (mass loss).
Results/Conclusions
Dispersal added a small fraction of new cells to the resident community (0.026%); however, immigrating taxa strongly altered bacterial community composition and functioning. While the numbers of immigrating cells entering the surface soil via the three routes were similar, the composition of bacteria dispersing through these routes greatly differed. Further, dispersal through rain/air and local vegetation altered community assembly on the fresh leaf litter, whereas dispersal from the bulk soil did not. Dispersal from any route initially increased decomposition rate, although communities closed to dispersal eventually reached the same rate. Our experiment contributes to emerging evidence that bacterial dispersal is limited in terrestrial systems and is the first to show that dispersal routes and rates influence community assembly in surface soils.