Collembola effects on plant mass and nitrogen acquisition by ash seedlings ( Fraxinus pennsylvanica)

Abstract

We studied the effects of varied collembolan numbers on three compensatory mechanisms of nutrient uptake: fine root mass, endomycorrhizal development, and physiological uptake capacity. We grew ash ( Fraxinus pennsylvanica) with or without the arbuscular mycorrhizal fungus Glomus intraradices, with 0, 10 or 50 initial Collembola ( Folsomia candida). After 83 d root NH 4 + and NO 3 − uptake rates, endomycorrhizal development, and plant biomass were determined. Plant mass increased with Collembola number. Collembola interacted with mycorrhizae in their effects on N uptake and leaf N. Collembola in the absence of mycorrhizal roots were associated with lower N uptake and leaf N at 10 than at 0 or 50 initial Collembola. In contrast, Collembola in the presence of mycorrhizal roots were associated with the highest rate of N uptake and leaf N at 10 versus 0 or 50 initial Collembola. Hence as initial Collembola number increased, the relative importance of root system traits that determined N uptake changed from root physiological uptake capacity, presence of mycorrhizal roots, to fine root biomass.