武夷山不同海拔森林表层土壤轻组有机质特征

土壤轻组有机质是土壤有机质的重要组分，研究轻组有机质在不同森林生态系统土壤中的变化规律对理解土壤有机质形成与转换具有重要意义。以福建省武夷山国家级自然保护区不同海拔的常绿阔叶林（海拔600 m）、针阔混交林（海拔1000 m）和针叶林（海拔1400 m）为研究对象，利用密度分组方法分离了表层（0-5 cm和5-10 cm）土壤轻组有机质，研究了不同海拔森林土壤轻组有机质特征及其影响因素。结果表明：针阔混交林表层土壤的轻组有机质含量大于针叶林和常绿阔叶林（P < 0.05），并且轻组有机碳的含量变化亦是如此（P < 0.05），而轻组有机氮的含量无显著差异（P > 0.05）。表层土壤对应土层的轻组C：N大于土壤C：N，针阔混交林轻组C：N和土壤C：N均大于其他林分类型。0-5 cm与5-10 cm土层针阔混交林的轻组有机碳、氮储量均大于针叶林和常绿阔叶林（P < 0.05），并且针阔混交林的轻组有机碳、氮储量所占土壤有机碳与总氮的比重均大于其余两种林分。0-10 cm土层针叶林土壤有机碳与总氮含量与储量最高，并随海拔降低而减小，但差异不显著（P > 0.05）。相关分析结果表明，轻组有机碳、氮储量与SOC、DOC、MBC和细根生物量具有显著相关关系（P < 0.05），而与年凋落物量无关（P > 0.05），说明地下细根可能是土壤轻组有机质的重要来源。因此，在未来气候和植被变化共同作用下，地下细根对土壤轻组有机质的形成可能具有不可忽视的作用。

Characteristics of light fraction organic matter in surface soil of different altitude forests in Wuyi Mountain

Soil light fraction organic matter is an important component of soil organic matter. It is crucial to understand the relationship between soil organic matter and climate change by studying the variation of light fraction organic matter along an elevation gradient in subtropical China. Taking evergreen broad-leaved forest (EBF), mixed coniferous and broad-leaved forest (BCF), and coniferous forest (CF) at different altitudes (from low to high elevation) in Wuyishan National Park in Fujian Province as research objects, the light fraction organic matter in surface soil (0-5 cm and 5-10 cm) was separated by density fractionation analyses, as well as the characteristics of light fraction organic matter and its influencing factors in different forest ecosystems were studied. The results showed that the content of light fraction organic matter in BCF was higher than that in CF and EBF in 0-5 cm and 5-10 cm soil layers (P < 0.05). The pattern of the content of light fraction organic carbon was similar to the light fraction organic matter, but there was no significant difference in light organic nitrogen content (P > 0.05). The light fraction C/N was greater than soil C/N, and the light fraction C/N and soil C/N in BCF were greater than those of other forest types in the same soil layer. In 0-5 cm and 5-10 cm soil layer, the storage of light fraction organic carbon and nitrogen in BCF were higher than those in CF and EBF (P < 0.05), and the contribution of light fraction organic carbon and nitrogen to soil organic matter in BCF was higher than that of the other two forests. The contents and storage of soil organic carbon and total nitrogen in CF was the highest in 0-10 cm, and decreased with the decrease of altitude, but the difference was not significant (P > 0.05). The correlation analysis showed that the storage of light fraction organic carbon and nitrogen was significantly correlated with soil organic carbon, dissolved organic carbon, microbial biomass carbon and fine root biomass (P < 0.05), but not annual litterfall (P > 0.05), suggesting that root derived organic matter might be an important source of light fraction organic matter in soil. Therefore, we concluded that belowground sources may play an important role in regulation of the formation of light fraction organic matter in soil under future climate change.