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The influence of soil fauna on nitrogen mineralization and decomposition in soil formed under western redcedar, western hemlock, sitka spruce and douglas-fir forests on the west coast of Vancouver Island Pratt, Jessica

Abstract

The influence of soil fauna on indices of N mineralization and decomposition in soil developed under four tree species (western redcedar, western hemlock, Sitka spruce and Douglas-fir) from the west coast of Vancouver island, B. C. was evaluated over a 5- month period. The soil was either defaunated, or given an assemblage of mites, collembola, nematodes and enchytraeids extracted from soil collected from the study site, or given the latter plus one millipede (Harpaphe haydeniana haydeniand). The experiment was carried-out in pots (microcosms) in a greenhouse. Water-leached, KC1- extractable and total N concentration (leached N plus KCl-extractable N plus plant N content) increased with increasing faunal community complexity. The effect was more apparent in the presence of the millipede. The millipede enhanced the rate of decomposition to a statistically significant degree. Rates of N mineralization did not differ significantly between combinations of soil fauna and soil type (tree species). Both decomposition and microbial biomass were significantly enhanced in the presence of H. h.haydeniana. (and other fauna) in Sitka-spruce soils. Western redcedar soil mineralized the most N. The use of cabbage plants as indicators of N availability did not prove to be a good choice; plant biomass was extremely variable and not related to other measures of N availability. The abundance of soil fauna was low and this may have reduced the potential for statistically significant differences between fauna treatments.

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