Lignin Distribution And Degradation Status In Soils In A Subtropical Mixed Forest In Mt.Badagongshan

Lignin is one of the most abundant aromatic compound in the terrestrial ecosystem,and is an important component of soil organic matter(SOM).Lignin has long been considered as the major source of stable organic carbon in soil,its content and degradation status has vital influence on the size and stabilization of soil C pool.In many studies,lignin has been used as an index to trace the dynamic of soil C pool.Currently,with global climate warming,the research on the dynamic of stable C has been more importance,and lignin has been one of the most studied macromolecules in natural environments.The fate of lignin in soils was regulated by various factors.However,the effects of plant communities on lignin turnover in subtropical forest ecosystems was not clear.Although scientists paid more enthusiasm to organic carbon(C)stored in subsoil due to the large pool size of subsoil C and its preponderant role in global C cycle,yet there still have some controversies on the distribution and degradation of lignin in different soil depths.The physical protection of lignin by soil aggregates is the dominant mechanism of of lignin stabilization in soils.However,most researches on the content and degradation of lignin in different size soil aggregate factions were mainly conducted in croplands.The relation between lignin and soil aggregate fractions in subtropical forest is not clear,which was importance to understand the C fluxes in terrestrial ecosystems.Additionally,we know little about the effects of plant community and soil depth on the distribution of different size aggregate fractions and the protection of soil aggregates on lignin.In this study,we choose four major plant communities in a subtropical mix forest in Badagongshan(BDGS)National Nature Reserve in central China:Carpinus fargesii(CF),Fagus lucida(FL),Cyclobalanopsis multinervis(CM)and Schima parviflora(SP),respectively.We collected soil samples at three depth ranges:0-10 cm,10-30 cm and 30-60 cm in each plant community,and fractionated soil samples into four size aggregate fractions:>2 mm,1-2 mm,0.25-1 mm and<0.25 mm.We measured the content and degradation status of lignin in all the bulk soil and soil aggregate fractions through CuO oxidation method.The lignin characteristics in plant litter and fine root were also measured in this study.The results showed that:1)Lignin content and chemical signature of plant litter varied with plant communities.The plant litter in two deciduous plant communities CF and FL have higher lignin content than the two evergreen plant communities CM and SP.Plant litter in CF and FL also have higher S/V,C/V and lower(Ac/Al)s and(Ac/Al)v than CM and SP.2)Plant community had significant effects on lignin content in deep soil,but not in the top two layer.The differences in lignin characteristics among plant communities in soils inherited some of the biochemical signature of lignin in litter,but in a diminished magnitude.These results suggest that different plant communities have different decomposition rates of lignin leading to similar outputs.Lignin content decreased with soil depth,but the biochemical signature of lignin was not significantly different among soil layers for all communities,which suggests that vertical movement of lignin within the soil profile is very likely a key process causing this similar biochemical signature.3)The distribution of aggregate fractions differed with plant community,but not with soil depth.Lignin content increased with deceased size of aggregates,however, the degradation status is similar among the four aggregate fractions.Results suggested that lignin has different turnover patterns in aggregate fractions:smaller aggregates is the preferential stored place of lignin,while bigger aggregates have more instability compound and faster dynamics.4)The effects of plant community and soil depth on lignin characteristics in aggregates are similar with their effects on lignin characteristics in bulk soil.The effects of plant community on lignin in aggregate fractions are not significant in top two layers.Lignin content of the same aggregate fraction sizes decreased with increased soil depths,but the differences of degradation status are not siganificant.These results indicated that the concentration and chemical signature of soil lignin in subtropical forests are influenced not only by vegetation and soil attributes,but also hydrological processes in the forest ecosystems.These new knowledge remind us that we should fully consider all environmental factors in precipitation rich forest ecosystems when studying lignin distribution and dynamics.