ASSESMENT OF WATER REPELLENCY ON BACTERIAL COMMUNITIES IN URBAN SOILS
Burga Braun, Uta Böckelmann, Elisabeth Grohmann, Ulrich Szewzyk.
Department of Environmental Microbiology, University of Technology, Franklinstrasse 29, D-10587
Berlin, Germany. burga.braun@tu-berlin.de
Soil water repellency has been recognized as a problem throughout the world. During the last few
years, millions of ha non wettable soils have been identified and recent studies suggest that water
repellent soils are the rule rather than the exception in many regions. Water repellency is an important
phenomenon in soil systems as it prevents water from infiltrating into the soil. Therefore it influences
soil chemical and physical properties which are important for many functions in ecosystems. A natural
function of soil is such as the habitat function for soil microorganisms. Bacteria live in soil water,
including the film of moisture surrounding soil particles. They are pivotal in the soil environment as
they control transformations and mineralization of natural compounds and xenobiotics. The microbial
community composition influences soil processes. Changes in soil wettability represent a significant
source of stress for microbial communities and alter the composition, growth and activity of soil
microorganisms (Denef, K. et al., 2001).This requires investigating the habitat function for
microorganisms. With the objective of the influence of water stress on microbial composition we
analyzed the bacterial community of an urban soil. We focus on the influence of water repellency on
microbial composition and activity.
Our experimental sites are located in the urban park Tiergarten in the centre of Berlin. This site is
characterized by a distinct developed heterogeneity of water repellency. So far, a soil profile of this site
was investigated by ARDRA and BIOLOG (Braun, B. et al., 2006). Hydrophilic and hydrophobic soil
samples were taken from the Ah-horizon for direct investigations and microcosm experiments. The
effect of water stress upon the diversity, culturability and activity of bacterial communities has been
investigated by cultivation techniques and molecular methods, such as BIOLOG and DGGE.
Cultivation of soil samples on 3 different media resulted in higher CFU numbers in water repellent
zones than in wettable zones. The total number of bacteria showed no significant differences between
both areas. DGGE based DNA fingerprints of total bacterial community DNA of wettable and non
wettable zones revealed two distinct clusters with a similarity of about 87 % by DGGE, respectively.
BIOLOG data revealed differing substrate utilization patterns for hydrophilic and hydrophobic areas.
No moisture related changes in CFU, total cell counts and active bacteria were observed in microcosm
experiments. In this soil, water stress had no influence on total bacterial community composition of this
soil, determined by DGGE.
References:
Braun, B. et al. (2006). Appl. Soil Ecol. 31 (3), 267-279.
Denef, K. et al. (2001). Soil Biol. & Biochem. (33) 1599 – 1611.