Understory plant species-specific effects on subarctic soil fertility

Although climate is the primary driver of soil fertility, plant functional traits can alter soil properties, creating a feedback between plants and soil fertility. In the lichen woodlands of the northern boreal forest, this feedback may be exemplified by slow growing ericaceous shrubs producing leaf litter that creates nutrient poor soils. We examined the soil of a lichen woodland in an area where fire had removed the organic layer 26 years previously and monospecific patches of ericaceous and non-ericaceous shrubs had developed, and the soil in an intact forest under the same species. In the burn site, soil inorganic N levels were four times higher under Salix candida Willd. than under Empetrum nigrum L. Soil from under S. candida in the forest also had a higher rate of respiration than soil under either ericaceous shrub. A growth assay with Leymus mollis, which is known to respond to nutrient additions in this region, showed twice as much growth in soil taken from under S. candida, regardless of whether the soil was collected from the forest or burn site. These results show that plant species can be a strong driver of soil fertility at a small spatial scale, even under harsh climatic conditions.