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

Abstract

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.

Polycyclic aromatic hydrocarbon transformation with laccases of a white-rot fungus isolated from a Mediterranean schlerophyllous litter

“…Thus particularly high amount of various phenolic compounds can be found in forest litters in this area (Racon et al, 1988). Under these drastic conditions, certain microbial species -mainly white-rot fungi-are able to transform phenols, which are recalcitrant molecules, via phenoloxidases such as laccases.…”

Comparative leaf decomposition within the holm oak complex

“…Thus the observed increase in weight from living to senescent leaves has been probably underestimated and cannot be explained by a sampling bias. Rather it is hypothesized that tannins, which oak leaves have accumulated during their entire life [24,26], will become totally or partly oxidized during the senescence of foliage [8], which will increase the areal weight of leaves before they fall.…”

Occurrence of Bacillus species on evergreen oak leaves

“…Adaptation to leaf surfaces could also be due to other selective factors such as water limitation, presence of a waxy surface making the attachment of cells or spores more difficult, or toxic leaf compounds [15].…”

“…One of the most widely studied bacilli, Bacillus thuringiensis [8][9][10] was found in the phylloplanes of temperate-climate trees [10]. Secondly, as Bacillus strains have been reported to be involved in the degradation of aromatic components [11][12][13][14], they could participate in situ to the degradation of evergreen oak leaves which contain a great deal of lignin and tannins [15].…”