Plant polyphenols - assessing trait conservation and litter decomposition of Chinese tree species on a secondary metabolite level

Background/Question/Methods

As important secondary metabolites in leaves, it has been suggested that plant polyphenols play a key function as defense from herbivory and microbial attack but there have been only few comparative studies across a range of species to test these ideas. In particular, little is known about the fate of phenolic compounds in the course of leaf litter decomposition. We asked how leaf litter decomposition of different species is related to total content of phenolics. Additionally, we tested how mixtures of litter from different species varying in total content of phenolics affects litter decomposition. We hypothesized that the decomposition rate of leaf litter increases as the contents in phenolics decreased due to microbial degradation.

We sampled leaves of 20 tree species out of 10 families. Additionally, we made use of a litter decomposition experiment, in which leaf litter of nine species was used from one species or from a mixture of two or three species in different combinations and was sampled at five time steps. Total phenolics content was determined using Prussian Blue Assay. Tannin content was assessed using a modified version of the Radial Diffusion Assay. Further traits were obtained from the BEF-China database.

Results/Conclusions

We found that the contents in total polyphenols and tannin were more phylogenetically conserved than other leaf traits. For the two secondary metabolites, the factors ‚Family‘ and ‚Genus‘ together explained approximately 90% of the variation within the data, whereas all other analyzed traits showed a much higher within-species variation. In the decomposition experiment we encountered a decrease in total phenolics and tannin content, which however is strongly depended on other leaf traits (such as leaf dry matter content). The results of our study provide a better functional understanding of the role of polyphenols in litter decomposition and now allow to focus on specific phenolic compounds in future decomposition studies.