Data for AP RRs suggest a general reduction in AP activity (RRs < 1) by amendment with P across most soils in O and B horizons in hardwood and softwood forest types (Fig. 2 and 3.). Response ratios for AP in soils amended with P and þNþP ranged from 0.36 to 0.89 and 0.38e0.97, respectively (Fig. 2b, 2c). However, differences between RRs from
the treated and reference watersheds do not suggest an effect of long-term N-enrichment on the magnitude of AP response to P addition alone or in combination with N, except in the case of O horizon soil from softwoods.