Inhaltszusammenfassung

Microorganisms in soil have strong impact on the water status in soil. Bacterial biofilms may decrease pore diameters develop new pores. Due to the heterogeneity in soil samples, it is problematic to distinguish the effect of biofilm on pore diameters from other effects like SOM swelling. In this study, we used glass bead reactors as model soil system and inoculated them with a biofilm producing bacterial isolate to observe the effect of biofilm on pore size distribution under controllable co...Microorganisms in soil have strong impact on the water status in soil. Bacterial biofilms may decrease pore diameters develop new pores. Due to the heterogeneity in soil samples, it is problematic to distinguish the effect of biofilm on pore diameters from other effects like SOM swelling. In this study, we used glass bead reactors as model soil system and inoculated them with a biofilm producing bacterial isolate to observe the effect of biofilm on pore size distribution under controllable condition. The stepwise reduction of the particle size in the reactors is part of our approach to soil conditions. The 1H-NMR measurements were performed at 2 MHz with a Maran 2 (Resonance, UK) using a CPMG pulse sequence. Biofilm reactors with 3 mm and with 500 to 355 µm glass beads were inoculated with a biofilm producing isolate (closely related to Sinorhizobium sp. TB8-10-II, with 99% sequence identity). After an incubation time of 3 to 6 days, the biofilm reactors were measured fresh and airdried/rewetted with the 1H NMR. The dry masses of the biofilms were gained gravimetrically after biofilmdetachment. In the biofilmreactors with 3 mm glass beads, we found two peaks in the relaxation time distributions of reactors with biofilm (Figure A). Peak 1 represents water in the biofilm-matrix (300-600 ms) and suggests the origin of a new pore system within the biofilm-matrix. T2 of Peak 2 was in the range of free water (~2000 ms) and peak 2 accounts for water in the interparticular pore space. The amount of water in the fresh biofilm was proportional to dry mass of biofilm. This correlation was missing for the rewetted biofilm, suggesting structural changes due to drying. In the biofilmreactors with 500-355 µm glass beads, T2 of peak 2 shifted from 1035 ms (without biofilm) to 820 ms in the presence of fresh biofilm (Figure B). This suggests decreasing interparticular pore diameters caused by biofilm grown on glass bead surfaces.» weiterlesen» einklappen

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