Relationship between chemical characteristics of autumn-shed leaves and aquatic processing rates

Processing rates of autumn-shed leaves in aquatic habitats are highly variable. It has been hypothesized that these processing rates may, in part, be regulated by the concentrations of residual tannins in the leaves. Tests of this hypothesis have been inconclusive, and experimental designs may have been compromised by the use of both processing rates and tannin concentrations taken from a variety of sources using highly variable methods, sites, and experimental conditions. Here, processing rates of 48 species of deciduous leaves are measured using uniform conditions, and related to concentrations of leaf tannins, N, P, C:N, lignin, and toughness. The results indicate that condensed tannin, N, C:N, and lignin are significantly correlated with processing rates, although the predictive power of these simple relationships is weak. A multiple regression model using tannins, measured as total phenolics, N, and lignin explained almost 50% of the variation in processing rates, suggesting that the inhibition of processing by tannins is modified by other measures of leaf quality.