Abstract
Most studies on soil enzymes are focused on the upper horizons of the soil profile, even though they transform the soil organic matter at every depth of the soil profile. The aim of this work was to investigate the distribution of β-glucosidase (GLU), nitrate reductase (NR), urease (UR), phosphatase (PHA), dehydrogenase (DHA) and catalase (CAT) activity through 14 trunked soil profiles of the Luvisols formed from a glacial till. The content of microbial biomass carbon (MBC) as well as physicochemical properties such as organic carbon (CORG), total nitrogen (NTOT), available P, K and Mg, soil density and porosity, pH in KCl and fractional composition were also studied. In general, enzymatic activity was highest in the top 30 cm layer of the profiles and decreased progressively towards the deeper horizons. The exceptions were the NR activity, which was active only in the Ap horizon and whose activity decreased sharply to nearly zero in the Bt horizon and parent rock, and the PHA activity, which was highly active even in the parent rock depth. The decreased availability of carbon and nutrients was the main driver of decreases in microbial abundance and enzymatic activity with depth. The enzymatic activity, when expressed on a CORG and MBC basis, behaves differently compared to the activity expressed on a soil mass basis. The activity decreased (NR), increased (PHA, UR), showed no clear pattern (GLU) or the changes were not significant (DHA, CAT). The content of CORG, NTOT, K and PAVAIL generally decreased with depth, while for Mg, there was no clear direction in the profile distribution. Future studies to characterize the substrate distribution within the soil profile and enzyme stability will provide further insight into the controls on nutrient cycling and related enzymes throughout the soil profiles.
Highlights
Soil enzymes mediate decomposition of soil organic matter and catalyze the main processes in carbon, nitrogen and phosphorus transformations [1,2]
The distribution of enzymatic activity with depth indicates that soils demonstrate the most activity in the top 30 cm layer, which has the most favorable content of organic matter and substrates compared to the deeper soil horizons
The enzyme activity in some of the profiles in the study decreased systematically with the soil depth, while in some other profiles, there was a variation between the enzymes in the sharpness of the gradient, and there were no clear changes in the distribution of the enzymatic activity profile
Summary
Soil enzymes mediate decomposition of soil organic matter and catalyze the main processes in carbon, nitrogen and phosphorus transformations [1,2]. Each type of soil has its own characteristic pattern of specific enzymes and its own inherent level of enzymatic activity, which depends on its origin and development conditions and on the content of organic matter [5]. Some attempts have been made to determine the patterns of the distribution of the soil enzyme activity in various soil profiles, the relative importance of the factors that influence the level of their activity through a specific profile has not yet been clearly established [6,9]. These, in turn, are determined by the quantity and quality of plant residues and root exudates, which are the sources of energy and nutrients for soil microorganisms as well as the source of the substrates for the soil extracellular enzymes.
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