Characterization of the transformations of lignocellulosic structures upon degradation in planted soil

Analytical pyrolysis (AP) as well as chemical analysis, ESR, FTIR and UV/VIS-spectroscopy has been used to characterize effects of modification of industrial lignins (hydrolysis lignin and kraft lignin) with silicon-containing oligomers on their transformation in soil planted with timothy grass (Phleum pratense). Using Py-GC/MS it was shown that carbohydrate-originated admixtures of non-modified hydrolysis lignin were degraded preferentially during the first vegetation season (12 weeks), whereas the degradation of lignin moieties was developed during the second vegetation season (60 weeks of incubation). The modification of both hydrolysis and kraft lignins with Si-oligomers promotes degradation of lignin from the earlier stage of incubation in soil. After the first 12 weeks of incubation the G/S ratio in products from pyrolysis of residual Si-modified hydrolysis lignin has increased almost twice, whereas for non-modified hydrolysis lignin this ratio has not changed. At the same time, Si-modification prevented oxidation of lignin during the whole incubation duration: yields of CO2 and carbonyl-containing compounds upon pyrolysis of residues of Si-modified hydrolysis lignin were lower in comparison with those for the residues of non-modified lignin. Simultaneously with degradation, condensation of the lignins residual structure occurred, moreover in Si-modified hydrolysis lignin up to a higher extent than for non-modified lignin. For non-modified kraft lignin an aromatization and condensation of the structure was observed at earlier incubation time in comparison with hydrolysis lignin, and the effect of Si-modification in this case is not as potent as it is observed for hydrolysis lignin. Py-GC/MS data were used to define relationships between the changes in chemical structure of lignins and numbers of microorganisms in the timothy grass rhizosphere. Significant positive correlations were found between the development of humus-degrading bacteria population and the relative abundance of carbon dioxide in the lignin pyrolysis products as well as between numbers of humus-degrading fungi population and relative abundances of guaiacol and syringol.