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 o f low inputs of N in precipitation and the absence of initial soil N p ools, the pattern of N accumulation is strongly biologically controlle d. The simple successional sequence at Glacier Bay is dominated by two main species (Alnus sinuata and Picea. sitchensis), thus the influenc e these species have on N dynamics is more easily deduced than in more complex systems. Along a successional sequence in Glacier Bay, N mine ralization rates, foliage and soil C:N, and foliage and soil delta(15) N values in six sites ranging in age from 20 to 225 years old were exa mined. It is concluded that: (1) Alnus sinuata and Dryas drummondii de rived 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 delta(15)N val ues; (3) over time, organic soil N separates into two isotopically dis tinct pools which differ in their turnover rate; (4) the transition fr om 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 delta(15)N values. (C) 1998 Elsevier Science B. V. All rights reserved.