The effect of differences in soil water content on microbial and enzymatic properties across the soil profiles

The differences in soil water content across the soil profiles produce changes in soil microbial and enzymatic properties, which play a major role in the transformation of soil organic matter. Permanent water saturation contributes to the formation of gleyic/stagnic horizons which have reducing conditions, this leads to a depletion in soil oxygen and changes in soil properties. To assess the effect of water content, we compared soil properties in the gleyic/stagnic horizons to the oxidative layers, which occurred at the same/similar depth in other profiles. The enzymatic activity and the number of microbial groups were assessed in eight soil profiles located in central Poland.

The studied properties responded differently to the water content. As expected, nitrate-reductase activity and the nitrate content were significantly higher in gleyic/stagnic than in oxidative conditions, while the opposite trend was found for phenol oxidase, urease, N-acetyl-glucosaminidase activity and the fungi number. No clear response in the total bacteria and facultative anaerobic bacteria (Bfa) count toward oxidation-reduction conditions was found. The dehydrogenases did not have a higher activity in the gleyic/stagnic as compared to the oxidative horizons and did not correlate significantly with the Bfa count. Differences in enzyme activities may be caused by the fact that the variation in frequency and duration of the reducing conditions in the soils may be insufficient to affect the short-term dynamics of these enzymes. The higher activity of some hydrolases in the reducing horizons may also be associated with the greater carbon and nitrogen content in these horizons.