Interactions of Marsh Orchid (Dactylorhiza spp.) and Soil Microorganisms in Relation to Extracellular Enzyme Activities in a Peat Soil

The nature of the interactions between microbes and roots of plants in a peaty soil were studied in a laboratory-based experiment by measuring activities of β-glucosidase, phosphatase, N-acetylglucosaminidase, and arylsulphatase. The experiment was based on control (autoclaved), bacteria-inoculated, and plant (transplanted with Dactylorhiza) treatments, and samples were collected over 4 sampling intervals. Higher enzyme activities were associated with the bacteria-inoculated treatment, suggesting that soil enzyme activities are mainly of microbial origin. For example, β-glucosidase activity varied between 25-30μmol g^-1 min^-1 in the bacteria-inoculated samples whilst the activity of the control ranged between 4-12μmol g^-1 min^-1. A similar pattern was found for all other enzymes. At the end of the incubation, the microcosms were destructively sampled and the enzyme activities determined in bulk soil, rhizospheric soil, and on the root surface. Detailed measurement in different fractions of the peat indicated that higher activities were found in rhizosphere. However, the higher activities of β-glucosidase, N-acetylglucosaminidase, and arylsulphatase appeared to be associated with bacterial proliferation on the root surface, whilst a larger proportion of phosphatase appeared to be released from root surface.