Influence of soil texture on protozoa-induced mineralization of bacterial carbon and nitrogen

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Abstract
Texture affects pore space, bacterial and protozoan populations and their activity in soil. The objective of this study was to test the hypothesis that protozoa grazing on bacteria increase the mineralization of bacterial C and N more in coarse-textured soils than in fine-textured soils. The microcosm experiment consisted of samples from three sterilized Orthic Black Chernozemic soils (SiC, CL and SL) inoculated with Pseudomonos bacteria, two treatments (with and without protozoa), and five sampling dates. The Pseudomonas population was labelled in situ by adding glucose- 14C and KNO3-15N (day 0). A species of Acanthamoeba was added to the microcosms on Day 2. On Day 4 bacterial numbers in all three soils were approximately 3 × 109 g−1 soil. The greatest reduction of bacteria due to protozoan grazing occurred between day 4 and day 7. All soils showed increased CO2-14C evolution and NH4-15N mineralization due to protozoan grazing but the mineralization rate of labelled N in the SL soil was much greater than in the fine-textured soils. The effect of texture on protozoan grazing was not as marked between day 12 and day 37 as earlier in the incubation. Protozoan-induced effects were transient in the soils studied and were most apparent in the coarse-textured soil. Key words: 14C, 15N, N mineralization-immobilization, bacteria, organic matter, Typic Cryoboroll, porosity, protozoa

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