Effects of vegetation and soil organisms on soil nutrient dynamics in subalpine Abies lasiocarpa forests

Graduation date: 1999The broadest goal of the research covered in this thesis was to contribute\ud to our limited knowledge of high elevation forest soil ecology. Based on the reeds\ud of funding agencies, specific objectives were to examine 1) how climate-induced\ud Abies lasiocarpa ([Hook.] Nutt.) forest expansion affects soil nutrient pools, 2) the\ud effects of commonly observed non-ectomycorrhizal fungal endophytes on A.\ud lasiosiocarpa foliar nutrients and 3) how human activity impacts soil foodweb\ud components and associated nutrient dynamics in backcountry recreation areas\ud located in A. lasiocarpa forests. Experimental and observational emphasis was\ud placed on major plant nutrients and the soil organisms that strongly control the\ud storage and cycling of those nutrients.\ud Major plant nutrients were measured in soils collected in Washington and\ud Montana where high elevation A. lasiocarpa forests are expanding into adjacent\ud meadows. Analyses indicated a consistent pattern of meadow-to-forest decline in\ud P and an increase in the ratio of C to N, despite differences in parent material and\ud topography. The increasing C:N ratio likely reflects changes in litter chemistry\ud associated with forest expansion. The decrease in extractable P at the three\ud locations is consistent with estimates of annual P accrual in subalpine forest\ud biomass reported in other studies, supporting a hypothesis that the meadow-to-forest\ud decline represents a shift in P from abiotic to biotic pools.\ud As is typical of the Pinaceae, A. lasiocarpa is known to be ectomycorrhizal,\ud but recent observations by others of seedlings collected in subalpine meadows\ud revealed abundant vesicular-arbuscular mycorrhizae (VAM) and unidentified, non-ectomycorrhizal,\ud dark-septate endophytes (DSE). Root colonization by thee two\ud endophytes was induced in laboratory-grown seedlings of A. lasiocarpa. In the\ud case of VAM, the presence of a graminoid meadow species grown together with the\ud tree seedlings led to abundant root colonization and increased foliar P. Foliar P\ud in a treatment where growing medium contained DSE fungal inoculum plus organic\ud material was double that in treatments containing one or the other, but not both.\ud Soils from a degraded subalpine recreation site were analyzed to determine\ud whether nutrient limitation or soil foodweb shifts might be a factor in poor site\ud recovery. Samples collected from a severely compacted, devegetated campsite\ud were compared to samples from adjacent undisturbed areas. Disturbance-related\ud shifts were detected in soil nutrient pools and in the soil foodweb