Vertical changes in P-acquiring enzyme activities and microbial biomass in Luvisols – The effect of different types of agricultural land use and soil-forming processes

Abstract

The activities of enzymes involved in the transformation of soil organic P are rarely measured in soils below a 30 cm depth, even though substantial amounts of P are also stored in deep soils. Changes in soil microbial biomass and the activities of P-cycling enzymes with depth were determined across the eight Luvisol profiles in four agricultural land uses including lucerne, winter wheat, vineyards and orchards. The activities of acid phosphatase (AcP), alkaline phosphatase (AlP) and phosphodiesterase (PDE) were assessed, as was the microbial biomass carbon (MBC) and phosphorus content (MBP) as well as some physico-chemical properties (e.g. total organic carbon – TOC, total nitrogen – TN, available phosphorus – Pavail, bulk density, pH in CaCl2). Additionally, mass and morphological parameters of the plant roots were also determined. The highest enzymatic activity and microbial biomass C and P content were found in the surface and sub-surface horizons and decreased with depth to varying degrees in parallel to the changes in TOC and TN. The studied properties were primarily determined by means of the organic C content and availability in all genetic horizons, while the influence of the lessivage (clay content) was only clearly pronounced for AcP activity, which was significantly higher in the illuvial layers (E) as compared to the eluvial horizons (Bt) in most of the considered profiles. What is more, only AcP activity was significantly and positively related to the root biomass and the number of small roots in the plants. Although it was revealed that the particular plants being cultivated had a significant impact on AcP activity, the data should be interpreted with caution because other factors (e.g. mineral fertilization) may also contribute to this.