The 10-year effects of different regimes of repeated fertilization on fine roots, mycorrhizae, and soil mesofauna were evaluated in young stands of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) and interior spruce (Picea glauca [Moench] Voss, Picea engelmannii Parry, and their naturally occurring hybrids) in central British Columbia. Fine root attributes and mesofauna responded differently to repeated fertilization regimes at the pine and spruce study sites. The length and vigour of lodgepole pine fine roots, the abundance of active roots, and the percent mycorrhizal colonization decreased with fertilization, especially in the most intensive fertilization regime. In contrast, the fine roots of fertilized interior spruce increased in length and the relative abundance of active and mycorrhizal roots was unaffected by treatment. Repeated fertilization of lodgepole pine altered mycorrhizal community structure and reduced species richness (number of species) and diversity (evenness). However, fertilization had a relatively small effect on mycorrhizal community structure, richness, and diversity at the spruce site. Total Acari (mite) densities declined in the forest floor and upper mineral soil following intensive fertilization of lodgepole pine. In contrast, the density of mites in the soils under interior spruce responded positively to repeated fertilization. It is not possible to ascribe the different responses of fine roots, ectomycorrhizae, and soil mesofauna found at these two sites to a specific cause, nor is it possible to state with certainty that the previously reported differences in aboveground tree growth responses of pine and spruce at these two sites (small and large, respectively) are directly linked with the belowground changes. Root and soil biota characteristics at other lodgepole pine and spruce "maximum productivity" sites are currently being examined to further understand the possible relationship between tree species and above- and belowground changes following repeated fertilization and the functional relevance of these effects.
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Updated March 14, 2008