Impacts of repeated fertilization on fine roots, mycorrhizas, mesofauna, and soil chemistry under young interior spruce in central British Columbia

Abstract

We assessed soil biota and soil chemistry in a 20-year-old interior spruce ( Picea glauca × engelmannii) stand in the interior of British Columbia 10 years after initiation of annual fertilization. Treatments included an unfertilized control, ON1 (having received per hectare 800 kg nitrogen (N), 350 kg phosphorus (P), 400 kg potassium (K)), and ON2 (having received per hectare 1400 kg N, 350 kg P, 400 kg K). Micronutrients were added periodically. There was more mineralizable N and NO3-N in the forest floor and upper mineral soil of ON2 plots than in the controls or ON1. Forest floor NH4-N increased with each level of fertilizer application. Total forest floor N, total sulphur, and exchangeable magnesium were higher with both levels of fertilization than with the unfertilized control. For the forest floor, available P and exchangeable K were highest in ON1. Forest floor densities of Acari, Prostigmata, and Oribatida were greater in fertilized plots than unfertilized control plots. In mineral soil, only Oribatida increased significantly with fertilization. Fertilization increased fine root length in ON1 relative to the control and ON2, but ectomycorrhizal colonization did not differ among treatments. These results contrast with previously reported responses to similar fertilizer treatments under lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) in which negative responses of fine roots and soil biota to repeated nutrient additions were observed.