NONADDITIVE EFFECTS OF LITTER MIXTURES ON NET N-MINERALIZATION IN A SOUTHERN NEW-ENGLAND FOREST

In this study, we developed simple, phenomenological models that enabl ed us to examine whether litter mixtures of differing quality increase d, decreased, or had no effect on the rate of net N mineralization rel ative to a model that extrapolated the expected result assuming no int eraction among litters of differing quality. We found that the presenc e of low quality litter (e.g., litter with a high lignin:N ratio) held the rate of net N mineralization to a uniformly low level until > 70% of the litter mixture was dominated by species of high litter quality . After this point, there was a rapid increase in the rate of net N mi neralization. Although there was a relatively small difference in the predicted rate of net N mineralization (1 kg ha(-1) 28 d(-1)) between the two models tone assuming an interaction among litter types and the second, no interaction), applied over larger spatial and temporal sca les, this relatively subtle difference could lead to considerably diff erent estimated rates of N supply to saplings and canopy trees over th e course of forest succession. (C) 1998 Elsevier Science B.V.