Dissolved organic carbon and nitrogen relationships in forest litter as affected by nitrogen deposition

Dissolved forms of carbon and nitrogen have become recognized for their imp ortance in forest nutrient cycling. The role of dissolved organic carbon (D OC) as an energy source for microbial metabolism is of particular interest. A laboratory decomposition experiment was conducted to examine the relatio nship between potential increased N inputs (via acid deposition) and DOC pr oduction in the forest litter layer and subsequent effects on DOC availabil ity in the forest floor. Air-dried leaf litter (seven species) was treated with nitrogen (nitrate or ammonium) or deionized (DI) water at weekly inter vals throughout 15 weeks and leached with DI water at 1 or 2 week intervals . Leachate was analyzed for DOC, inorganic nitrogen (NO3--N and NH4+-N) and dissolved organic nitrogen (DON). Litter was analyzed for percent C, perce nt N, weight loss and percent cellulose and lignin. Nitrogen treatments did not greatly affect DOC,concentrations in litter leachate. Differences in D OC concentrations were primarily due to a wide range of initial litter chem istries, where species with high extractives and low lignin had the highest DOC leachate concentrations. Nitrogen treated samples showed greater weigh tless than controls although nitrate and ammonium treatments were not signi ficantly different. Between 6 and 39% of total carbon loss was leached as D OC. These findings suggest that different forest types could vary greatly i n the quantity of carbon consumed or released and that nitrogen inputs appe ar to affect this overall cycle by increasing respiration (as measured by w eight loss), rather than increasing DOC release into the soil solution. Fur ther examination of the fate of DOC as it moves down in the soil profile an d measurements of CO2 evolution during laboratory decomposition, are necess ary to better understand these processes. (C) 2000 Elsevier Science Ltd. Al l rights reserved.