Patterns in N dynamics and N isotopes during primary succession in Glacier Bay, Alaska

The primary successional sequence in Glacier Bay, Alaska represents a 230-year record of the development of nitrogen (N) dynamics. Because of low inputs of N in precipitation and the absence of initial soil N pools, the pattern of N accumulation is strongly biologically controlled. The simple successional sequence at Glacier Bay is dominated by two main species (Alnus sinuata and Picea sitchensis), thus the influence these species have on N dynamics is more easily deduced than in more complex systems. Along a successional sequence in Glacier Bay, N mineralization rates, foliage and soil C:N, and foliage and soil δ15N values in six sites ranging in age from 20 to 225 years old were examined. It is concluded that: (1) Alnus sinuata and Dryas drummondii derived most of their N through the fixation of atmospheric N; (2) under conditions of high N availability, differences among species in plant preference for ammonium or nitrate can be deduced from δ15N values; (3) over time, organic soil N separates into two isotopically distinct pools which differ in their turnover rate; (4) the transition from an alder-dominated to a spruce-dominated system results in slower N cycling; and (5) previous site conditions are an important factor in explaining patterns in δ15N values.