Impacts of repeated fertilization on components of the soil biota under a young lodgepole pine stand in the interior of British Columbia

We studied elements of the soil biota in a 24-year-old lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stand in interior British Columbia 10 years after initiation of annual fertilizer treatments. The treatments included an unfertilized control, ON1 (650 kg nitrogen (N), 400 kg phosphorus (P), 400 kg potassium (K)), and ON2 (1350 kg N, 400 kg P, 400 kg K). In the forest floor, the C/N ratio was lower in ON1 and ON2 than in the unfertilized control, while available P and exchangeable magnesium were higher; NO3 was higher only in ON2. In the upper mineral soil, available P was higher in ON1 and ON2, while NO3 was higher only in ON2. In both the forest floor and upper mineral soil, microbial activity was higher in ON1 than in the unfertilized control or ON2. In the forest floor and mineral soil, Acari density, especially Oribatida and Prostigmata, was higher in ON2 than in ON1 and the unfertilized control. In contrast, Collembola density, especially Hypogastruridae, increased in ON2 relative to that in other treatments. ON2 had less lodgepole pine fine-root length, fewer ectomycorrhizal roots, fewer active fine roots, more nonmycorrhizal fine roots, and a different ectomycorrhizal community structure than ON1 and the unfertilized control. These dynamic changes to the soil biota appear to reflect changes to the plant community in response to fertilization.