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Long-term fertilization effects on ectomycorrhizal community structure and fine root length in interior spruce forests

Hay, T.N. 2012. University of British Columbia-Okanagan

Abstract

Ever-present on the roots of appropriate host trees, ectomycorrhizas are pivotal in the survival and productivity of trees of interior British Columbia. Although ectomycorrhizal (ECM) fungi provide access to nutrients that would otherwise be unavailable to roots, nutrient supply can still limit above ground productivity of trees. Such nutrient constraints have led to the use of fertilization as standard practice for increasing tree yields in some parts of the world. Although much research has been completed on the short-term response of ECM communities to nitrogen enrichment, almost none has focused on responses to long-term fertilization treatments aimed at maximum tree productivity. In our study, the response of ECM fungal communities of three interior spruce (Picea glauca) stands in interior British Columbia to 10-15 yr of fertilization was studied. The treatments included (i) unfertilized control, (ii) annual fertilization (kg ha-1); to maintain 1% foliar N (iii) periodic fertilization (kg ha-1); 200N, 100P, 100K, 50 sulphur, 25 magnesium, 1.5 boron applied every 6 years. The study sites were located in three different biogeoclimatic zones: the moist, cold (SBSmc2), the moist cool (SBSmk1) and the wet cool (SBSwk1) variants of the Sub-Boreal Spruce zone of central interior British Columbia. Using morphological and molecular analysis, the identity of the dominant ECM fungal symbionts on the randomly-selected root tips was determined in order to characterize the ECM fungal community. Both ECM fungal diversity and richness differed amongst sites, but did not appear to be affected by fertilization. The relative abundance and frequency of Tylospora spp., one of the dominant genera in the community, were lower in plots exposed to annual fertilization at one of the sites. No overall effect on the ECM fungal community was observed in response to fertilization. As the periodic fertilization treatment more closely reflects operational modes of fertilization in these regions, these results suggest that large-scale fertilization could be established in the central interior of British Columbia without major disturbance to this important component of the soil microbial community.