Decomposition Dynamics Of Phenolics In Polygonum Viviparum Litter

Phenolic compounds are widely distributed in higher plants as secondary metabolites. They have been described as defence against herbivores, resistance to pathogens, and they also play an important role in the nutrient cycling in terrestrial ecosystems. The influences of phenolics to . nutrient cycling were achieved by the way of plant litter decomposition.In this study that performed in the alpine meadow of Tianzhu County, Gansu province, a polyphenol-rich forb, Polygonum viviparum, was selected as the research object. Phenolic compounds in the litter, was extracted and separated. The content of total phenolics and condensed tannin was measured. The complexation capacity of condensed tannin with proteins was tested. The type and content of low molecular weight phenolics was determined. The type of condensed tannins monomers was identified and the degree of polymerization of condensed tannin was analyzed. In a one-year field litter decomposition experiment, the seasonal decomposition dynamics of low molecular weight phenolics and condensed tannin were examined. The main results are as follows:(1) The total phenolic content in the recent P. viviparum litter was 18.63 mg GAE/g DW. The types of low molecular weight phenolic compounds in litter include gallic acid (GA), protocatechuic acid (PA), chlorogenic acid (CA), trans-ferulic acid (FA) and (+)-rutin (rutin). As the decomposition progress, the content of total phenolics and each low molecular weight phenolic in litter showed a decreased trend. In the spring and summer, each compound decreased rapidly.(2) The type of tannin in P. viviparum is condensed tannin. The condensed tannin content in recent litter was 15.39 mg STE/g DW. During the time of litter decomposition, the content of condensed tannin in litter exhibited a downward trend, and the protein-complexation capacity of tannins was also decreased. In the spring and summer, the content as well as the protein-complexation capability of condensed tannin was reduced rapidly.(3) The construction monomers of condensed tannin in P. viviparum are gallocatechin(GC), catechin (C), epigallocatechin gallate (EGCG) and epicatechin (EC). The degree of polymerization of condensed tannins increased gradually during the process of litter decomposition.The results in this litter decomposition experiments indicate that in the alpine meadow ecosystem, the decomposition process of phenolics in P. viviparum litter was mainly influenced by abiotic factors such as climate (temperature and precipitation) and biotic factors such as soil microbes, litter quality, phenolic structures and properties. In the winter, decomposition of phenolics by fungi may be dominated. While in the summer, leaching of soluble phenolics by increased precipitation and accelerated decomposition by enhanced soil microbe activities caused by higher temperature might be the mechanism.Studying the type and content dynamics of phenolic compounds during the process of P. viviparum litter decomposition could help to understand the effects of phenolics especially tannin on nutrient cycling. It might provide basis to explain the mechanism of phenolic-rich plant uptaking of nitrogen, and it will be valuable for the sustainable development of alpine meadow.