Bacterial soil communities affected by water-repellency

Soil water-repellency is a common phenomenon which occurs throughout the world. It prevents water from infiltrating into the soil and influences soil properties. The effects of water stress induced by water-repellency were investigated with respect to composition and culturability of bacterial communities in soils from an urban park in the centre of Berlin. The bacterial populations of wettable soil areas were compared to populations of repellent soil areas. The genetic diversity was analysed by denaturing gradient gel electrophoresis (DGGE) and the physiological diversity was investigated using plate counts and BIOLOG substrate utilization analysis.The application of cultivation and cultivation independent methods did not allow distinction between the composition of bacterial communities of soil areas with different wettability. Water-repellency did not affect BIOLOG and DGGE fingerprints as investigated by digital image analysis. Similarity analysis of DGGE profiles of the soil community from wettable and repellent zones revealed three distinct clusters of about 74%, 80% and 81% similarity, respectively. BIOLOG fingerprint patterns were similar as determined by average well colour development (AWCD). However, cluster analysis of BIOLOG data generated a dendrogram revealing three distinct clusters showing no separation related to soil wettability. Determination of total cell counts did not result in differences between both zones. Colony forming units (CFUs) showed significantly higher counts in wettable zones than in water-repellent zones. Sequencing of 38 excised bands from different DGGE profiles from wettable and repellent soil samples indicated the presence of typical soil bacteria: the bands were attributed to clones of the classes of Cyanobacteria, Actinobacteria, Chloroflexi and the phylum Firmicutes.