Influence of nitrogen on cellulose and lignin mineralization in blackwaterand redwater forested wetland soils

Microcosms were used to determine the influence of N additions on active ba cterial and active fungal biomass, cellulose degradation and lignin degrada tion at 5, 10 and 15 weeks in soils from blackwater and redwater wetlands i n the northern Florida panhandle. Blackwater streams contain a high dissolv ed organic C concentration which imparts a dark color to the water and cont ain low concentrations of nutrients. Redwater streams contain high concentr ations of suspended clays and inorganic nutrients, such as N and P, compare d to blackwater streams. Active bacterial and fungal biomass was determined by direct microscopy; cellulose and lignin degradation were measured radio metrically. The experimental design was a randomized block. Treatments were : soil type (blackwater or redwater forested wetlands) and N additions (soi ls amended with the equivalent of 0, 200 or 400 kg N ha(-1) as NH4NO3). Red water soils contained higher concentrations of C, total N, P, K, Ca, Mn, Fe , B and Zn than blackwater soils. After N addition and 15 weeks of incubati on, the active bacterial biomass in redwater soils was lower than in blackw ater soils: the active bacterial biomass in blackwater soils was lower when 400 kg N ha(-1), but not when 200 kg N ha(-1), was added. The active funga l biomass in blackwater soils was higher when 400 kg N ha(-1), but not when 200 kg N ha(-1), was added. The active fungal biomass in redwater wetland soils was lower when 200 kg N ha(-1), but not when 400 kg N ha(-1), was add ed. Cellulose and lignin degradation was higher in redwater than in blackwa ter soils. After 10 and 15 weeks of incubation. the addition of 200 or 400 kg N as NH4NO3 ha(-1) decreased cellulose and lignin degradation in both we tland soils to similar levels. This study indicated that the addition of N may slow organic matter degradation and nutrient mineralization, thereby cr eating deficiencies of other plant-essential nutrients in wetland forest so ils.