Histological and chemical changes in tannic compounds of evergreen oak leaf litter

In evergreen oak leaves collected at a western Mediterranean site (Var, France), the amounts of both hydrolyzable and condensed tannins decrease through the depth of the leaf litter. The decrease in condensed tannins could be partly explained by the cellular degradation of the lower epidermis and the mesophyll of leaves, as observed in histological sections. However, the condensed tannins may also be degraded by microbial enzymes because their average molecular weight decreased by about 50%. In contrast, the decrease in hydrolyzable tannins seems to be initiated by microbial enzymatic action, which is then followed by the same degradation process described above.