FOREST BIOGEOCHEMISTRY AND PRIMARY PRODUCTION ALTERED BY NITROGEN SATURATION

Results from four intensive site-level manipulations acid one extensiv e field survey in northern temperate and boreal forests show a consist ent set of responses to chronic N additions. These include 1) initial and often large increase in net N mineralization followed by decreases , 2) increases in net nitrification. 3) increases in N concentration i n foliage, and 4) decreased Mg:N and Ca:Al ratios, and declining tree growth and vigor in all evergreen stands. These results are synthesize d into a set of proposed summary relationships that define the tempora l pattern of responses of N-limited systems to N additions.