Effects of season and four tree species on soluble carbon content in fresh and decomposing litter of temperate forests

Decomposition of plant material is an important component in the study of forest ecosystems because of its critical role in nutrient cycling. The turnover of nutrients in forest soil organic matter depends on, among other factors, a readily available supply of C for decomposer organisms. Levels of water soluble C in leachate from four species of forest floor material were compared at five sampling periods in 1988, and an assessment of correlations between the measured soluble C levels and levels of respired CO2, Co (potentially mineralizable C) and k (decay rate) was performed. Potential release of water-soluble C following freeze/thaw treatment was evaluated. Sugar maple (Acer sarcharum Marsh) leachate averaged 1.7 times more soluble C than leachate from Norway spruce (Picea abies (L.) Karst.), red pine (Pinus resinosa Ait.), and black locust (Robinia pseudoacacia L.). Average levels of soluble C for all samples in October were more than 2 times higher than those from July, August, September, and December, but soluble C levels did not generally correlate with CO2 evolved during 20-day laboratory incubations. Correlations between soluble C and C, and k were poor. Maple substrate collected before autumn leaf fall and treated to alternating cycles of freezing and thawing released significantly greater amounts of soluble C than either controls or samples held at a constant 4 degrees C. Post-leaf fall maple substrate yielded significantly greater soluble C values for each treatment, and treatment effects decreased in the following order: freeze/thaw > 23 degrees C > 4 degrees C. Levels of soluble C released from forest floor material depended on the species of substrate, and the degree of decomposition of the material, Cycles of freezing and thawing released additional soluble C. Initial decomposition of ''fresh'' soil organic matter by microorganisms may be triggered by the availability of a soluble C pool.