亚热带不同林分土壤表层有机碳组成及其稳定性

在浙江临安玲珑山选取了常绿阔叶林、马尾松林、板栗林和雷竹林4种林分,采用传统的化学方法与固态13C核磁共振(NMR)技术研究其土壤有机碳在不同粒径土壤颗粒中的分布规律和结构特征,探讨林分类别和管理措施对土壤有机碳含量及其结构的影响,为亚热带地区森林固碳和土壤碳库管理提供科学依据.结果显示:(1)土壤表层(0-20 cm)有机碳含量按以下次序递减:雷竹林＞常绿阔叶林＞马尾松林＞板栗林,且板栗林以粉黏粒结合态碳为主,其他林分土壤则以粗砂结合态碳为主；(2)13C NMR结果表明,阔叶林和马尾松林土壤有机碳中烷基碳所占比例最大,而雷竹林和板栗林则是烷氧碳比例最大,表明人工经营措施改变了土壤有机碳的成分组成；(3)随着土壤颗粒变细,有机碳中烷基碳比例增加,烷氧碳比例减少,A/O-A值和疏水碳/亲水碳值逐渐增大,表明颗粒越细,其结合的有机碳结构稳定性越高.

Composition and stability of organic carbon in the top soil under different forest types in subtropical China

Soil organic carbon (C)influences soil physical, chemical and biological properties that control nutrient cycling and consequently have important impacts on forest productivity and sustainability. Due to the important role of soil organic C in nutrient cycling of forest ecosystems and global C balance, there has long been an interest in understanding the effects of vegetation types and forest soil management on soil C pools. Four types of forest vegetations, including evergreen broad-leaved forest, Masson pine (Pinus massoniana), Chestnut (Castanea mollissima) forest and Phyllostachys praecox forest, on Linglong mountain located in Lin''an county, Zhejiang Province, China, were selected to study the distribution and chemical composition of soil organic C using chemical analysis and solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy. The results showed that the contents of soil organic C in the 0-20 cm soil layer under different forest types decreased in the order: Phyllostachys praecox forest >evergreen broad-leaved forest >Masson pine forest >Chestnut forest. Content of soil organic C under Phyllostachys praecox forest was significantly higher than that under other three types of forests. However, there were no significant differences in content of soil organic C content among other 3 types of forests. The proportion of C combined with coarse-sand fraction was the greatest in the soils under evergreen broad-leave, Masson pine and Phyllostachys praecox forests, while the soil under Chestnut forest contained a larger proportion of C combined with clay and silt fraction. The ¹³C NMR spectra showed that alkyl C had the highest intensity among the four C functional groups in the soils under the evergreen broad-leave and Masson pine forests, while O-alkyl C was the predominant organic C in soils under Phyllostachys praecox and Chestnut forests. These results indicate that forest management practices can affect chemical composition of soil organic C. The ratios of alkyl C/O-alkyl C (A/O-A) and Hydrophobic C/Hydrophilic C, and alkyl-C content increased, but the O-alkyl-C content decreased, with the decrease in soil particle-sizes. In other words, the finer particles (e.g., silt and clay) contain more stable soil organic C than the coarse particles (e.g., coarse and fine sands) do. However, relationship between aromaticity of soil organic C and soil particle size fractions was not consistent in soils among four forest types. There were significant differences in aromaticity, A/O-A and Hydrophobic C/Hydrophilic C between Phyllostachys praecox forest and other forests. Content and stability of soil organic C appeared to be closely related to the contents of silt and clay in soils. Therefore, soils with high content of silt and clay can potentially build up greater amount and more stable soil organic C. In conclusion, vegetation type, management practices, and soil tillage could significantly affect the distribution and stability of organic C in different particle-size fractions as well as the contents of organic C of forest soils.