Zhang Tian-Yu, Zhang Yan, Jia Qi, Zhou Shuang, Li Tian-le, Li Cong-Xiao, Liu Fu-de
School of Environmental Science and Safety Engineering, Tianjin University of Technology, Tianjin 300384, China.
Tianjin Academy of Eco-Environmental Sciences, Tianjin 300191, China.
Huan Jing Ke Xue. 2024 Nov 8;45(11):6527-6537. doi: 10.13227/j.hjkx.202312202.
Different vegetation types may affect the accumulation and transformation of soil organic carbon （SOC）, but it is unclear whether the organic carbon fixation is realized by litter input and/or root control of environmental factors and dissolved organic matter （DOM） of soils. In this study, the spatial distribution characteristics of easily oxidizable organic carbon （EOC）, dissolved organic carbon （DOC）, particulate organic carbon （POC）, mineral-bound organic carbon （MAOC）, and their seasonal variations in the surface soil （0-10 cm） were studied in different vegetation zones of the arbor forest （at the upper position）, the mixed forest of arbor and shrub （at the middle position）, and the waterfront vegetation （at the bottom position） in the ecological embankment of Duliujian River, Tianjin, China. The spatial distribution characteristics of soil DOM components and their seasonal changes were also analyzed by combining UV-visible spectroscopy and 3D fluorescence spectroscopy. The results showed that： ① The accumulation of SOC was significantly higher in the waterfront vegetation than in the arbor forest and the mixed forest of arbor and shrub in summer, whereas the opposite was true during the spring season. It was indicated that the root input of the soil was the key driving factor for determining the accumulation of SOC in summer, whereas the input quality of above-ground litters was more important for the sequestration of SOC in spring. ② Differences in DOM fractions explained the fixation and transformation pathways of SOC in different seasons, with humus-derived DOM in spring promoting the transformation of DOC to POC and MAOC and microbial-derived DOM in summer advancing the transfer of EOC to MAOC under the action of microorganisms. ③ Soil physicochemical properties had less direct influences on SOC, which preferentially affected SOC accumulation by regulating the composition as well as the chemical structure of soil DOM. ④ The structural equation modeling indicated that water content （MC） and total phosphorus （TP） were directly involved in SOC transport and transformation, whereas ammonium nitrogen （NH-N）, nitrate nitrogen （NO-N）, electrical conductivity （EC）, available phosphorus （AP）, pH, K, and Na indirectly affected SOC accumulation mediated by DOM from humus and microbial sources. In summary, the present study elucidated that the trade-off mechanisms affecting SOC sequestration in the critical functional zone along the land-river ecotone, and the results can provide theoretical support for further exploring the constructive methods of ecological corridors and the pathways of carbon sequestration and sink enhancement in the "watershed-estuary-offshore" system of the coastal rivers.
不同植被类型可能影响土壤有机碳（SOC）的积累与转化，但尚不清楚有机碳固定是通过凋落物输入和/或根系对环境因子及土壤溶解有机物质（DOM）的调控来实现的。本研究在中国天津独流减河生态堤岸的乔木林（上部）、乔灌混交林（中部）和滨水植被（下部）不同植被区，研究了表层土壤（0 - 10 cm）中易氧化有机碳（EOC）、溶解有机碳（DOC）、颗粒有机碳（POC）、矿物结合有机碳（MAOC）的空间分布特征及其季节变化。同时结合紫外可见光谱和三维荧光光谱分析了土壤DOM组分的空间分布特征及其季节变化。结果表明：①滨水植被中SOC的积累在夏季显著高于乔木林和乔灌混交林，而在春季则相反。这表明土壤根系输入是夏季决定SOC积累的关键驱动因素，而地上凋落物的输入质量对春季SOC的固存更为重要。②DOM组分的差异解释了不同季节SOC的固定和转化途径，春季腐殖质来源的DOM促进了DOC向POC和MAOC的转化，夏季微生物来源的DOM在微生物作用下推动了EOC向MAOC的转移。③土壤理化性质对SOC的直接影响较小，其主要通过调节土壤DOM的组成和化学结构来影响SOC积累。④结构方程模型表明，含水量（MC）和总磷（TP）直接参与SOC的迁移和转化，而铵态氮（NH-N）、硝态氮（NO-N）、电导率（EC）、有效磷（AP）、pH、K和Na则通过腐殖质和微生物来源的DOM间接影响SOC积累。综上所述，本研究阐明了影响陆地 - 河流交错带关键功能区SOC固存的权衡机制，研究结果可为进一步探索生态廊道建设方法以及沿海河流“流域 - 河口 - 近海”系统中碳固存和汇增强途径提供理论支持。
