中国亚热带4种林分类型凋落叶分解过程中^(13)C NMR波谱特征

Changes in ^(13)C NMR Spectroscopy of Leaf-Litter during The Decomposition in Four Subtropical Forest Types in Southern China

【目的】旨在揭示不同结构碳组分在凋落叶分解过程中的作用机制。【方法】以浙江省临安玲珑山毛竹人工林、马尾松天然次生林、杉木人工林和青冈天然次生林凋落叶为研究材料,采用常规化学分析方法与固态13C核磁共振技术探讨其分解过程中的全C和全N含量及不同形态C化合物相对含量的变化。【结果】经12个月的分解,4种林分凋落叶的质量损失率表现为青冈天然次生林(53.80%)>马尾松天然次生林(52.69%)>杉木人工林(48.31%)>毛竹人工林(41.17%);在分解过程中,凋落叶中的N含量逐渐升高,C含量和C/N比逐渐降低,烷氧碳的相对含量显著减少(9.34%~15.48%,P<0.05),而芳香碳和羰基碳分别增加25.14%~37.37%和0.75~2.08倍(P<0.05);凋落叶中的C含量与凋落叶质量残存率之间,C/N比与凋落叶质量残存率之间均极显著正相关(r=0.901 0~0.984 0,P<0.01),而N含量与凋落叶质量残存率极显著负相关(r=-0.921 1^-0.983 1,P<0.01),凋落叶中的烷氧碳相对含量与凋落叶质量残存率呈极显著正相关(r=0.808 2~0.962 2,P<0.01),芳香碳相对含量与凋落叶质量残存率间、羰基碳相对含量与凋落叶质量残存率间均极显著负相关(r=-0.779 9^-0.936 6,P<0.01),除马尾松人工林外,其他林分凋落叶的烷基碳相对含量与凋落叶质量残存率均无显著相关性。【结论】4种林分凋落叶中,青冈天然次生林凋落叶降解最快;在有机碳中,烷氧碳、芳香碳和羰基碳在凋落叶降解过程中起着决定性的作用;13C NMR波谱技术更利于监测凋落叶分解过程中不同结构碳组分的变化,从而更深刻认识凋落叶的分解机制。

【Objective】The leaf-litter,as a main part of the litter in a forest ecosystem,is a main source of soil organic matter and plays a key role in the carbon cycle of the forest system. The purpose of this study is to reveal the action mechanism of carbon fractions with different structures during the decomposition process of leaf-litter.【Method】This study selected the leaf-litter under Moso bamboo（ Phyllostachys edulis） plantation,Masson pine（ Pinus massoniana） natural secondary forest,Chinese fir（ Cunninghamia lanceolata） plantation and Cyclobalanopsis glauca natural secondary forest in the Linglong mountain,Lin＇an county,Zhejiang province as study materials,and determined the contents of total C and N,and different forms of carbon compounds in the leaf litter of different stands by using chemical analysis and13 C NMR spectroscopy technology. 【Result 】 Mass loss rates of the leaf-litter of 4 forest stands decreased in the order：Cyclobalanopsis glauca natural secondary forest（ 53. 80%） Pinus massoniana plantation（ 52. 69%） Cunninghamia lanceolata natural secondary forest（ 48. 31%） Phyllostachys edulis plantation（ 41. 17%） 12 months after decomposition of leaf-litter. During decomposition process of the leaf-litter, N contents in the leaf-litter increased gradually,while the contents of C and ratios of C/N decreased gradually; the relative contents of alkoxy carbon reduced by9. 34%-15. 48%（ P〈0. 05）,while the relative contents of aromatic carbon and carbonyl C increased by 25. 14%-37. 37% and 0. 75-2. 08 times（ P〈0. 05）,respectively. Both C contents and ratios of C/N in leaf-litter correlated positive and significant with the leaf-litter mass remaining rates（ r = 0. 901 0-0. 984 0,P〈0. 01）,while the N contentsin leaf litter correlated positive and significant with the leaf-litter mass remaining rates（ r =-0. 921 1--0. 983 1,P〈0. 01）; The contents of O-alky1 C in the leaf-litter correlated positive and significant with the leaf-litter mass remaining rates（ r = 0. 808 2-0. 962 2,P〈0. 01）,while the contents of aromatic C and carbony1 C in the leaf-litter both correlated negative and significant with the leaf-litter mass remaining rates（ r =-0. 779 9--0. 936 6,P〈0. 01）; the contents of alkyl C in the leaf litter did not correlate with leaf-litter mass remaining rates except leaf-litter of Pinus massoniana natural secondary forest.【Conclusion】In the leaf litter under 4 forest stands,leaf-litter from Phyllostachys edulis plantation were more easier to degrade than other three stands. In the total organic carbon,the components of alkoxy C,aromatic C,and carbonyl C play a decisive role in the degradation of leaf-litter.13 C NMR spectroscopy technique was found to be more accurate in understanding the decomposition mechanism of leaf-litter than conventional matrix indicators during monitoring the changes of different carbon components in the leaf-litter decomposition process.