Articles | Volume 2, issue 4
SOIL, 2, 499–509, 2016
SOIL, 2, 499–509, 2016

Original research article 04 Oct 2016

Original research article | 04 Oct 2016

Enzymatic biofilm digestion in soil aggregates facilitates the release of particulate organic matter by sonication

Frederick Büks and Martin Kaupenjohann Frederick Büks and Martin Kaupenjohann
  • Chair of Soil Science, Department of Ecology, Technische Universität Berlin, Berlin, Germany

Abstract. The stability of soil aggregates against shearing and compressive forces as well as water-caused dispersion is an integral marker of soil quality. High stability results in less compaction and erosion and has been linked to enhanced water retention, dynamic water transport and aeration regimes, increased rooting depth, and protection of soil organic matter (SOM) against microbial degradation. In turn, particulate organic matter is supposed to support soil aggregate stabilization. For decades the importance of biofilm extracellular polymeric substances (EPSs) regarding particulate organic matter (POM) occlusion and aggregate stability has been canonical because of its distribution, geometric structure and ability to link primary particles. However, experimental proof is still missing. This lack is mainly due to methodological reasons. Thus, the objective of this work is to develop a method of enzymatic biofilm detachment for studying the effects of EPSs on POM occlusion. The method combines an enzymatic pre-treatment with different activities of α-glucosidase, β-galactosidase, DNAse and lipase with a subsequent sequential ultrasonic treatment for disaggregation and density fractionation of soils. POM releases of treated samples were compared to an enzyme-free control. To test the efficacy of biofilm detachment the ratio of bacterial DNA from suspended cells and the remaining biofilm after enzymatic treatment were measured by quantitative real-time PCR. Although the enzyme treatment was not sufficient for total biofilm removal, our results indicate that EPSs may attach POM within soil aggregates. The tendency to additional POM release with increased application of enzymes was attributed to a slight loss in aggregate stability. This suggests that an effect of agricultural practices on soil microbial populations could influence POM occlusion/aggregate stability and thereby carbon cycle/soil quality.

Short summary
Soil aggregate stability and POM occlusion are integral markers for soil quality. Besides physico-chemical interactions, biofilms are considered to aggregate primary particles, but experimental proof is still missing. In our experiment, soil aggregate samples were treated with biofilm degrading enzymes and showed a reduced POM occlusion and an increased bacteria DNA release compared with untreated samples. Thus, biofilms are assumed to be an important factor of POM occlusion in soil aggregates.