Non-additive effects of litter mixtures on net N mineralization in a southern New England forest

In this study, we developed simple, phenomenological models that enabled us to examine whether litter mixtures of differing quality increased, decreased, or had no effect on the rate of net N mineralization relative to a model that extrapolated the expected result assuming no interaction among litters of differing quality. We found that the presence of low Ž . 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 Ž net N mineralization. Although there was a relatively small difference in the predicted rate of net N mineralization 1 kg y1 y1. Ž . ha 28 d between the two models one assuming an interaction among litter types and the second, no interaction , applied over larger spatial and temporal scales, this relatively subtle difference could lead to considerably different estimated rates of N supply to saplings and canopy trees over the course of forest succession. q 1998 Elsevier Science B.V.