The Vernal Dam: Plant‐Microbe Competition for Nitrogen in Northern Hardwood Forests

Abstract

Nitrogen (N) uptake by spring ephemeral communities has been proposed as a mechanism that retains N within northern hardwood forests during the season of maximum loss. To understand better the importance of these plants in retaining N, we followed the movement of ¹⁵NH₄⁺ and ¹⁵NO₃^— into plant and microbial biomass. Two days following isotope addition, microbial biomass represented the largest labile pool of N and contained 8.5 times as much N as Allium tricoccum L. biomass. Microbial immobilization of ¹⁵N was 10—20 times greater than uptake by A. tricoccum. Nitrification of ¹⁵NH₄⁺ was five times lower in cores containing A. tricoccum compared to those without the spring ephemeral. Spring N retention within northern hardwood forests cannot be fully explained by plant uptake because microbial immobilization represented a significantly larger sink for N. Results suggest that plant and microbial uptake of NH₄⁺ may reduce the quantity of substrate available for nitrification and thereby lessen the potential for NO₃^— loss via denitrification and leaching.