Biodegradation Of Lignin And The Effect On Its Indicative Parameters

Lignin is the main component of vascular plants, which chemically connected tocellulose and hemicellulose in the fiber walls, providing strength and rigidity to theplant structures as well as resistance to the biodegradation. For the character that lig-nin just comes from land plant and its low degradability, it is extensively used as abiomarker to trace the source of terrestrial organic matter (TOM) in soil, water andsediment. From the indicative parameters, we can infer the amount of TOM, the ter-restrial vegetation in different ages, by these information, we can reconstruct the pa-leoenvironment and paleoclimate.As a popular biomarker, lignin has many advantages. However, evidences indi-cate that when we use lignin to estimate the source of TOM, this method can not pro-vide undisputable results, one of the main reasons is that biodegradation during theprocess of transportation and burial leads to the changes of lignin parameters. It istherefore very important to study the biodegradation of lignin to estimate the effect.The main purpose of this thesis is to study the effect of biodegradation on.ligninindicative parameters. We first screened some ligninolytic fungi from soil sample, andused them to degrade wood flour in12weeks. During this process, we sampled every4weeks, determined the changes of lignin structure and the amount of lignin phenols,the main conclusions are:1. The screened3fungi from soil samples were named F3, F5and F6. By mac-roscopic observation of colonies, microscopic observation of hyphae and colorful re-actions of enzyme, we proved the three fungi are white-rot fungi.2. We used FTIR to determine the changes of wood structure after degradation.The result showed that oxidation is the important process during degradation. We ob-served the degradation of cellulose and hemicellulose with no damage of the aromaticring skeleton from the spectrogram of the samples degraded by F3, while the spectro-grams of F5and F6showed the damage of the aromatic ring skeleton, indicating thedifferent degradation mechanism. 3. After CuO oxidation of sound wood flour, we focused on8lignin monomers:3vanillyl phenols,3syringyl phenols and2cinnamyl phenols. The total yields of cin-namyl phenols did not exceed0.1%of the wood dry weight, while the yields of sy-ringyl and vanillyl phenols were about6.0%and1.6%, which corresponds to the factthat the wood flour was from the woody tissue of an angiosperm plant.4. During12weeks of degradation process, all of the lignin indicative parameterschanged. The dry weight of wood flour,∑8, S/V and C/V ratios continuously de-creased while (Ad/Al)v and (Ad/Al)s increased. Different fungi led to different extentof changes.5. In the process, Ad/Al kept increasing while the corresponding S/V and C/V ra-tios kept decreasing progressly. These changes will definitely affect lignin as a bio-marker of terrestrial input.For the important effect of biodegradation on the change of lignin indicative pa-rameters as we found, more attention should be given to lignin biodegradation whenusing lignin as a biomarker of TOM. We advise that the value of Ad/Al ratio shouldfirst be checked before using other parameters, to assess the extent of lignin degrada-tion. The solution to this problem is to use new parameters which will not be affectedseriously by lignin degradation, or combine other methods such as pollen analysis,δ13C, C/N, biogenic silicon and so on to obtain more information about the sample,which will increase the confidence for lignin analysis.