Fig. 4. Relationship to green age of (A) microbial biomass (MB) per unit mass of particulate organic matter (POM) and mineral fraction (MF) and (B) soil mass composed of POM. Soils are air-dried and from greens sampled in 1997 and 1999. Each data point is a single observation. *, **, and ***, both model and slope are significant at P = 0.05, 0.01, and 0.001, respectively.