Potthast, K. | Search bioRxiv

bioRxiv2025

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. HighlightsO_LIRainwater flow paths are important carriers for organic matter and microorganisms. C_LIO_LIThroughfall and stemflow contained high abundances of microbial cells. C_LIO_LIBacteria contributed up to 11 % and 33 % to exported carbon and nitrogen. C_LIO_LIBacterial taxa were selectively mobilized by throughfall, stemflow and seepage. C_LI

microbiology↗

bioRxiv2020

Drought and rewetting events enhance nitrate leaching and seepage-mediated translocation of microbes from beech forest soils

Nitrification in forest soils is often associated with increased leaching of nitrate to deeper soil layers with potential impacts on groundwater resources, further enhanced under scenarios of anthropogenic atmospheric nitrogen deposition and predicted weather extremes. We aimed to disentangle the relationships between soil nitrification potential, seepage-mediated nitrate leaching and the vertical translocation of nitrifiers in soils of a temperate mixed beech forest in central Germany before, during and after the severe summer drought 2018. Leaching of nitrate assessed below the litter layer and in 4, 16 and 30 cm soil depth showed high temporal and vertical variation with maxima at 16 and 30 cm during and after the drought period. Maximum of soil potential nitrification activity of 4.4 mg N kg-1 d-1 only partially coincided with maximum nitrate leaching of 10.5 kg N ha-2. Both ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were subject to translocation by seepage, and AOB decreased at least by half and AOA increased by one to three orders of magnitude in their abundance in seepage with increasing soil depth. On the level of the total bacterial population, an increasing trend with depth was also observed for Cand. Patescibacteria while Bacteroidetes were strongly mobilized from the litter layer but poorly transported further down. Despite stable population densities in soil over time, abundances of AOA, AOB and total bacteria in seepage increased by one order of magnitude after the onset of autumn rewetting. Predicted future higher frequency of drought periods in temperate regions may result in more frequent seepage-mediated seasonal flushes of nitrate and bacteria from forest soils. Moreover, the observed translocation patterns point to taxon-specific differences in the susceptibility to mobilization, suggesting that only selected topsoil derived microbial groups are likely to affect subsoil or groundwater microbial communities and their functional potential.

microbiology↗