亚热带地区3种典型林分土壤DOM数量及光谱特征

Soil DOM Quantity and Spectral Characteristics of Three Typical Forest Soils in Subtropical China

可溶性有机质(DOM)是土壤有机质库中最为活跃的部分,也是土壤有机库中对环境变化最敏感的部分,它参与了有机质在土壤中的腐殖化和微生物的新陈代谢等一系列生物地球化学过程。因此,在调节土壤养分周转和森林生态系统碳氮循环过程中起到重要的桥梁作用。采用水浸提法,结合紫外-可见光谱、荧光光谱、傅里叶红外光谱等技术,探讨了亚热带米槠人促林(AR)、米槠次生林(SF)、杉木人工林(CF)的土壤DOM的数量和光谱特征,以期深入评价森林转换对不同林分土壤肥力及其养分有效性的影响。结果表明:各林分A层土壤DOC、DON浓度均高于B层。B层土壤中,米槠人促林的DOC浓度显著低于其他2种林分(P<0.05),而各林分A层土壤的DOC和DON浓度并无显著差异。各林分A、B层土壤DOM的芳香化指数无显著差异。米槠次生林A层土壤DOM的荧光发射光谱腐殖化指数(HIXem)、荧光效率(Feff)显著高于其他2种林分(P<0.05),其HIXem分别是米槠人促林、杉木人工林的1.3、1.2倍,其Feff分别是米槠人促林、杉木人工林的2.7、2.5倍。三维荧光光谱表明,各林分A层土壤DOM主要以类腐殖酸物质为主;B层土壤中,米槠人促林和杉木人工林以类蛋白物质为主。各林分土壤的荧光指数(FI)均大于1.4,且B层土壤DOM的鲜度指数(β∶α)均高于A层。傅里叶红外光谱表明,米槠人促林土壤DOM没有羧酸的吸收,土壤pH最高;而米槠次生林土壤羧酸的相对含量最高;杉木林土壤DOC含量少,芳香化合物、羧酸等难分解物质相对富集。综合来看,除了建群树种的影响外,林下植被对土壤肥力的作用也很突出。

Dissolved organic matter（DOM） is the most active pool of soil organic matter,sensitive to environmental changes,involved in many biogeochemical processes such as humification and microbial metabolism in soil. Therefore,it plays an important role in regulating soil nutrient turnover and carbon and nitrogen cycling in forest ecosystems. In this study,we used UV-Vis spectroscopy,Fluorescence spectroscopy and Fourier transform infrared spectroscopy,to investigate the quantity and spectral characteristics of DOM extracted from soils of a human assisted naturally regenerated forest of Castanopsis carlesii（AR）,a secondary broadleaved forest of Castanopsis carlesii（SF） and a plantation of Cunninghamia lanceolata（CF） in subtropical China. The aim was to evaluate the effect of forest conversion on soil fertility and nutrient availability. Results showed that the concentrations of dissolved organic carbon（DOC） and dissolved organic nitrogen（DON） in layer A were higher than those in layer B for each stand. DOC concentrations in layer B significantly lower in AR than in SF and CF（P 0. 05）,whereas DOC and DON concentrations in layer A showed non-significant difference among three forests. Within a stand,no significant difference in soil aromatic index（AI） was observed between soil A and B layers. For layer A,SF showed significantly higher humification index（HIXem）and fluorescence efficiency（Feff） than the other two stands（P 0. 05）,1. 3 times of SF and 1. 2 times of CF for HIXem,respectively,as well as 2. 7 times of SF and 2. 5 times of CF for Feff,respectively. The three-dimensional fluorescence spectrum revealed that DOM in layer A of all stands were mainly humic acid-like substances; while DOM in layer B of AR and CF was dominated by protein-like substance. Fluorescence index（FI） of all soil samples was more than 1. 4,and the freshness index（β ∶ α） increased with soil depth. AR soil DOM demonstrated no absorption of carboxylic acid in FTIR spectrum,consistent with its highest soil pH; in contrast SF soil DOM contained the highest proportional content of carboxylic acid. More refractory substances were enriched in CF soil DOM,accompanied by its lowest DOC content. Overall,besides overstory trees,understory vegetation also plays an essential role in enhancing soil fertility.