Study On Evolution Law Of Different Carbon Fraction And Phytolith-Occluded Organic C In Leaf Litter From Four Forest Species With The Decomposition In Subtropics Of China

Leaf litter as a main component of forest litter is a major source of soil organic matter in forest ecosystems.Quantity and quality of organic matter in a soil ecosystem is of utmost importance in regulating of soil quality and global climate change.Phytolith-occluded organic carbon?PhytOC?is a stable form of organic carbon and goes back into the soil after the plant dies or withers,thus affecting storage of the soil stable carbon pool.In this study,13 C nuclear magnetic resonance?NMR?was used to study the changes in the signal intensities of different carbon compounds,and alkali spectrophotometry method was applied to determine the PhytOC concentrations in the leaf litter during the decomposition process from four typical forest types?Moso bamboo stands,MBS;Masson pine stands,MPS;Chinese fir stands,CFS;Evergreen broad-leaf stands,EBS?.The main results were as follow:?1?The decomposition process of leaf litter from four forest types was analyzed.The results showed that leaf litter mass loss rates after the decomposition process of 12 months were in the following order: EBS?53.80%?> MPS?52.69%?> CFS?48.31%?> MBS?41.17%?,indicating that the leaf litters from MBS and CFS were more difficult to degrade than those from MPS and EBS.The semi-decomposed time of four leaf litters ranged from 10.5 to 14.5 months,and 95% litter decomposition time 3.91 to 5.27 years.With the time of litter decomposition,the N contents in these four kinds of forest litters increased gradually,whereas the C contents and C/N decreased gradually.The C contents and ratios of C/N in different leaf litters was significantly positive correlated with leaf litter mass remaining rates?r=0.9010-0.9840,p<0.01,n=12?,while N contents in different leaf litter showed significantly negative correlation with leaf litter mass remaining rates?r=-0.9211--0.9831,p<0.01,n=12?.?2?¹³C-NMR spectral characteristics of four forest type leaf litter during the decomposition were studied.The results showed that the signal intensities of carbonyl C was significantly increased by 0.75-2.08 times,and ones of aromatic C was also slightly increased by 25.14-37.37%,but ones of alkyl C and O-alkyl C fluctuated with increases or decreases.The signal intensities of O-alkyl C,aromatic C,or carbonyl C in leaf litter showed a significantly positive correlation with leaf litter mass remaining rates?r = 0.8800-0.9301,p< 0.01,n =12?,but signal intensities of alkyl C in leaf litter was not significantly correlated with leaf litter mass remaining rates with an exception of leaf litter from MPS.In contrast,¹³C-NMR spectroscopy techniques were more effective than conventional matrix indicators in detecting the changes of different carbon components in leaf-litter decomposition process and thus in understanding the decomposition mechanism of leaf-litter.?3?Change characters of Phytolith-occluded organic C in leaf-litter from four forest type leaf litter during the decomposition process was studied.The results showed that the decomposition process of leaf litter contributed to the accumulation of silicon and Phytoliths.The Phytolith contents in the leaf litter from MBS,MPS,CFS,and EBS ranged from 139.61 to 169.69,from 7.43 to 10.98,from 7.12 to 11.04,and from 7.55 to 10.54 g·kg-1,respectively.The organic carbon contents in Phytolith of leaf litter from MBS,MPS,CFS,and EBS ranged from 24.52 to 29.29,from 81.55 to 94.23,from 109.81 to 123.71 and from 80.94 to 91.59 g·kg-1,respectively.There were significant differences?p<0.05?in Phytolith contents and PhytOC contents in leaf litter between MBS and the other 3 forest stands.Also,there were significant differences?p<0.05?in Monthly release rates of Phytolith and PhytOC from leaf litter from MBS and the other 3 forest stands.In conclusion,leaf litters from MBS and CFS were more difficult to degrade than those from MPS and EBS.With the time of litter decomposition,the content of O-alkyl C decreased continuously,and the proportion was higher than the other carbon components,which played a decisive role in the litter decomposition.¹³C-NMR spectroscopy techniques were more effective to understand the decomposition mechanism of leaf-litter deeply.The leaf litters from MBS have the highest content of Phytolithand the lowest content of PyhtOC among these Four Forest Species.Leaf litters of all species have carbon sequestration potential,among which litter from MBS owned the highest potential.Decomposition rate,Phytolith productivity and capacity of carbon sequestration were the main factors resulting in the differences in forest soil PhytOC contents.