不同稻虾种养模式土壤溶解性有机质光谱特征

Spectral characteristics of soil dissolved organic matter in different rice-crayfish cultivation modes

  • 摘要: 稻虾种养的农业活动显著改变了田间生物化学因子, 土壤溶解性有机质(DOM)是其中之一。本研究利用紫外-可见吸收光和三维荧光光谱技术, 耦合平行因子分析, 对有环沟式稻虾轮作和共作、无环沟式稻虾共作和传统稻作4种稻虾种养模式土壤DOM的特征进行了研究。结果显示, 不同稻虾种养模式土壤DOM紫外吸光度和比吸收系数均低于传统稻作, 光谱斜率比(SR)均值为0.9~2.0; 254 nm和365 nm处紫外吸光度的比值(E2/E3)在无环沟稻虾共作模式中最小, 水稻单作中E2/E3值相对于稻虾种养模式大; 300 nm和400 nm处紫外吸光度的比值(E3/E4)在稻虾种养模式均<3.5, 水稻单作>3.5。4种模式的荧光指数>1.9, 腐殖化指数<4, 自生源指数为0.6~0.7。不同模式均解析出2个类蛋白质组分(类络氨酸、类蛋白物质)和2个类腐殖质组分(腐殖酸、类腐殖质), 与生物源密切相关的类络氨酸组分占比较高且与其他组分均呈负相关, 其余组分相互呈正相关。上述结果中, 紫外-可见吸收光谱参数表明稻虾种养降低了土壤DOM的腐殖化程度、芳香性和物质组成, 稻虾种养土壤腐殖质类DOM腐殖酸为主, 水稻单作以富里酸为主; 4种模式的土壤DOM既有内源也有外源, 其中无环沟稻虾共作模式土壤DOM分子量最大, 且有一定外源性特征, 说明土壤保肥能力较好, 在4种模式中综合效益最佳; 三维荧光光谱分析表明不同模式下土壤DOM的物质组成无明显差异, 研究认为这与农田管理措施的间接影响等有关, 占比较高的络氨酸组分来源不同于其他组分, 可能与微生物对DOM或其他物质的分解转化有关, 而腐殖酸、类蛋白物质和类腐殖质组分很可能有高度的同源性; 不同种养模式之间的淹水差异通过影响溶解性有机碳(DOC)和DOM的释放, 从而影响种养模式之间DOM光谱特征。

     

    Abstract: Rice and crayfish co-cultivation is the largest cultivation mode in China and is an important part of ecological agriculture. However, in the process of cultivation, the activities changed the physical and chemical properties of field soils, which had a significant effect on the change in organic matter. Dissolved organic matter (DOM), one of the most active components of organic matter, is also the subject of modification, but there are few related studies on the characteristics of modified dissolved organic matter. Therefore, in this study, ultraviolet-visible (UV-Vis) absorption spectra and three-dimensional fluorescence spectra were used to calculate different spectral parameters combined with parallel factor analysis (PARAFAC) to study the characteristics of soil DOM under four rice and cultivation modes (integrated rice-crayfish rotation system with ring groove, RS1; integrated rice-crayfish system with ring groove, RS2; integrated rice-crayfish system, RS0; traditional rice monoculture, MR). The results revealed that there were weak shoulder peaks at 260–280 nm in the UV-Vis absorption spectrum of soil DOM in all modes, and the absorbance decreased with increasing wavelength and gradually approached zero. The UV-Vis absorption spectral parameters SUVA254 (specific absorption coefficient) and UV254 (UV absorbance at wavelength 254 nm) of soil DOM in different rice and crayfish cultivation modes (RS1, RS2 and RS0) were lower than those of traditional rice monoculture (MR). The E2/E3 (ratio of UV absorbance at 254 nm to 365 nm) value was smallest in RS0, and the SR (spectral slope ratio) values of the two co-cropping patterns (RS2 and RS0) were averaged from 0.5 to 2.0. For all modes, the mean value of fluorescence index >1.9, humification index < 4, biological index = 0.6−0.7. All rice and crayfish cultivation modes had resolved two protein-like components (C1, C3) and two humic-like components (C2, C4), C1 accounted for a higher proportion and was negatively correlated with other components, and the remaining components were positively correlated with each other. The principal component analysis identified four effective components, which were arranged according to the contribution rate: PC1 represented the concentration and aromaticity of DOM; PC2 represented the biological characteristics, molecular weight and degree of humification of DOM; PC3 represented the protein components and autogenic features in DOM; PC4 represented the molecular structure of DOM. The results showed that many unsaturated aromatic structure molecules existed in the soil DOM of all modes. Rice and crayfish cultivation reduced the degree of humification and aromaticity of soil DOM. The RS0 mode had the largest molecular weight of soil DOM and certain exogenous characteristics; the soil fertilizer retention ability was better, and the comprehensive benefit was the best among the three rice and crayfish farming modes. There was no significant difference in the material composition of soil DOM under different modes, which was related to the indirect effects of agricultural management practices. The source of C1 was different from that of other components, which may be related to the decomposition and transformation of DOM by microorganisms. Additionally, the difference in flooding was one of the main reasons for the difference in soil DOM characteristics; the soil releases DOM and DOC through flooding, which significantly affects the characteristics of soil DOM. In production practice, attention should be paid to the application of organic fertilizers, which can maintain soil fertility, increase DOM and microbial diversity, maintain soil fertility, and monitor the status of contaminants in soil and crops on farmlands.

     

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