Rainwater-driven transport of matter and microbes from phyllosphere to soil in a temperate beech forest

In forest ecosystems, the transport of organic matter including microbial cells by throughfall and stemflow represents a central linkage between the phyllosphere and soil. However, the extent and taxon-specificity of rainwater-mediated vertical transfer of microorganisms, and its relevance for matter fluxes is sparsely understood. We investigated the rainwater-driven transport of bacteria and its contribution to matter transport in bulk rainfall, throughfall, stemflow and seepage in a temperate deciduous forest and compared the transported communities to those in phyllosphere and soil. Throughfall-mediated cell fluxes equaled those in seepage below the litter layer, pointing to a substantial above-ground translocation of bacteria. Bacterial cells contributed up to 11 % and 33 % to the exported total organic carbon and total nitrogen, respectively. Bacteria affiliated with Pseudomonadaceae, Oxalobacteraceae, Hymenobacteraceae, and Sphingomonadaceae were differentially transmitted from the canopy with increased abundances in throughfall and stemflow compared to bulk rain. A small fraction of shared taxa pointed to the import, proliferation and mobilization of selected bacterial taxa between neighboring ecohydrological compartments. The genetic potential of the transported bacterial communities was strongly linked to organic matter degradation particularly of carbohydrates and proteins. Our findings extend our understanding of rainwater-mediated vertical matter transport in forest ecosystems and highlight the contribution of microbial cells to this transport especially in above-ground compartments. Strong shifts in community composition and abundance of the transported taxa between throughfall, stemflow and soil seepage are linked to differences in source communities but may also point to different mechanisms of cell detachment across compartments.