可溶性有机质(DOM)是森林生态系统能量循环的主要载体, 在碳循环过程中发挥着重要的作用。为了深入了解植被恢复后土壤DOM的变化和结构特征, 在典型红壤侵蚀区福建省龙岩市长汀县河田镇选取不同恢复年限的马尾松(Pinus massoniana)林为研究对象, 利用光学技术对比分析了不同恢复年限(0年, 13年, 31年)马尾松林保留芒萁(Dicranopteris dichotoma)覆盖地、去除芒萁覆盖地和林下裸地土壤DOM光谱特征。结果表明: 未治理地(Y0)、恢复13年(Y13)和恢复31年(Y31)马尾松林芒萁覆盖地土壤可溶性有机碳(DOC)含量分别是林下裸地的7.61倍、4.83倍和5.47倍, 去除芒萁一年后, 土壤DOC的含量显著下降, 但仍分别是林下裸地的1.84倍、4.12倍和4.73倍; 芒萁覆盖地土壤DOM的芳香化指数(AI)和腐殖化指数(HIX)均显著高于林下裸地, 而波长在250 nm和365 nm处的紫外可见光光度值之比(E₂:E₃)的趋势与之相反, 去除芒萁一年后, AI和HIX降低显著, 表明芒萁覆盖地土壤DOM腐殖化和芳香化程度更高, 分子量更大; 林下裸地DOM红外光谱中特征峰明显不如林下芒萁覆盖地丰富, 其含有更多的羟基、羧酸类, 以及碳水化合物中的烷氧基等结构简单、易迁移的物质, 去除芒萁一年后, DOM红外光谱特征峰无明显变化, 表明芒萁是土壤DOM数量和结构的主要影响因素, 而这种影响是一个长期缓慢的过程。从DOM光谱分析结果可知, 芒萁覆盖下土壤DOM的分子量更大, 结构更复杂, 易于被土壤胶粒吸附, 维持其化学稳定, 利于土壤有机碳积累。由此可见, 芒萁在土壤有机碳积累过程中具有积极的作用。

Aims Dissolved organic matter (DOM) is the most active component of organic matters in soils, and plays an important role in carbon cycles. It is a mixed organic compound with varying molecular sizes and weights. We aimed to explore the impacts of Dicranopteris dichotoma coverage on quantity and structure of DOM after vegetation restoration in severely eroded red soil region. Methods A typical sequence of vegetation restoration (Y0, without ecological restoration; Y13, ecological restoration for 13 years; Y31, ecological restoration for 31 years) was selected as the research object in Hetian Town, Changting County, Fujian Province, China. At each experimental site, soils were subject to three treatments—NRd, not removed D. dichotoma; Rd, removed D. dichotoma; and CK, control, and the effects of D. dichotoma on the spectral characteristics of DOM were evaluated.Important findings The results indicated that the quantity of soil DOC under NRd treatment of the Y0, Y13 and Y31 was 7.61, 4.83, and 5.47 times higher than their CK treatment, respectively. The Rd treatment had significantly lower DOC than that under NRd treatments, and it was 1.84, 4.12, and 4.73 times higher than their CK treatments, respectively. Thus the D. dichotoma had exerted significant effects on the quantity of soil DOM. The Aromaticity index (AI), emission fluorescence spectrum humification index (HIX_em) and synchronous fluorescence spectrum humification index (HIX_syn) of DOM under the NRd treatment were significantly higher than those of the CK treatments in Y13 and Y31, respectively. However, the ratio of ultraviolet-visible light absorption photometric quantity at 250 nm wavelength to ultraviolet-visible light absorption photometric quantity at 365 nm wavelength (E₂:E₃) had an opposite trend. It showed that the DOM structure in soils covered by D. dichotoma contained more aromatic nucleus and had higher aromaticity and humification, and DOM molecular was larger. In addition, the AI and humification index (HIX) of DOM under the Rd treatment was significantly decreased compared with the NRd treatment. Similar results were observed by analysis of emission and synchronous fluorescence spectrum, and by the Fourier infrared transmission spectrum analysis. These results suggest that D. dichotoma had positive impacts on the complexity of DOM structure, but it was a long and slow process. The DOM spectral analysis showed that the soil DOM covered by D. dichotoma had a stable and complex structure and was easily adsorbed by soil colloid. As a result, Dicranopteris dichotoma had a positive effect on the accumulation of soil organic carbon.