不同来源有机肥释放的溶解有机质粒径分布与光谱特征

  【目的】  研究不同来源有机肥释放的溶解有机质 (DOM) 的粒径分布与光谱特征，为有机肥在农业生产中的应用及DOM后续环境行为的研究提供理论指导。  【方法】  本研究选择海藻、羊粪、虾肽以及小麦秸秆生物炭4种有机肥，提取有机肥中的DOM (<0.7 μm)。利用超滤分级技术对提取的DOM进一步区分为 <1 kDa、1～100 kDa、100 kDa～0.2 μm和0.2～0.7 μm 4个粒级，使用总有机碳 (TOC) 分析仪测定各粒径DOM的含量并使用傅里叶变换红外光谱 (FTIR)、紫外?可见吸收光谱 (UV-Vis) 和三维荧光光谱 (3D-EEM) 进行光谱表征。  【结果】  从全量 (粒径<0.7 μm) 溶解有机碳(DOC)来看，小麦秸秆生物炭 (308 mg/kg)<虾肽 (1060 mg/kg)<海藻 (1266 mg/kg)<羊粪 (2989 mg/kg)。供试有机肥中不同粒径的DOC所占比例和含量差异明显，均以最小粒径 (<1 kDa) 所占比例最高，除海藻为47%外，其余有机肥处理皆达到50%及以上。4种不同来源有机肥DOM的紫外和荧光特征值表明，4种有机肥的荧光指数 (FI) 和自生源指数(BIX)随着DOM粒径的减小而增大，而SUVA₂₅₄、SUVA₂₆₀和腐殖化指数 (HIX)随着DOM粒径的减小而减小。虾肽DOM各粒径的类蛋白组分含量高且主要为内源DOM，自生来源有机质丰富，生物可利用性高；羊粪DOM各粒径受人类活动影响较大；而小麦秸秆生物炭的DOM大粒径(>100 kDa)组分的FI<1.4，表明其大粒径DOM主要为外源性的，自身生产和微生物活动贡献相对较低。此外，尽管海藻、羊粪和虾肽各粒径的DOM的HIX值随着粒径的减小而逐渐减小，除虾肽DOM的<1 kDa组分外，其腐殖化程度依旧较高 (HIX>10)，而小麦秸秆生物炭小粒径DOM的HIX<4，表明小麦秸秆生物炭的小粒径DOM疏水组分含量高，腐殖化程度相对较低。荧光组分和红外光谱表明了4种不同来源有机肥DOM以类腐殖质物质为主，且含有大量氨基酸N—H键、O—H键和C—O键等官能团。  【结论】  依据有机肥释放的DOM的粒径分布和光谱特征，海藻、羊粪、虾肽有机肥中的DOM主要以小粒径为主，其腐殖化程度高，蛋白组分含量较低。小麦秸秆生物炭DOM的生物稳定性要高于其他有机肥，生物可利用性较低，因此，施加过量的生物炭不利于微生物对土壤DOM的降解利用；而虾肽来源有机肥的DOM类蛋白组分贡献最大，生物可利用性高，施用虾肽有机肥可能有利于微生物对土壤DOM的降解利用。

Size fraction distribution and spectral characteristics of dissolved organic matter derived from different organic fertilizers

  【Objectives】  The size fraction distribution and spectral characteristics of dissolved organic matter (DOM) released from different sources of organic fertilizers were studied to guide the application of organic fertilizer in agricultural production and the subsequent environmental effect of DOM.   【Methods】  The DOM in the aqueous solution of the different organic fertilizers (i.e., wheat straw biochar, shrimp peptide, seaweed and sheep manure) was classified by ultrafiltration classification technology. The content of each size fraction was determined by total organic carbon (TOC) analyzer, and the spectra were characterized by Fourier transformed infrared spectroscopy (FTIR), ultraviolet visible absorption spectroscopy (UV-Vis) and three-dimensional fluorescence spectroscopy (3D-EEM).  【Results】  In terms of total (<0.7 μm) dissolved organic carbon (DOC), the results were in order of wheat straw biochar (308 mg/kg) < shrimp peptide (1060 mg/kg)254, SUVA₂₆₀ and humification index (HIX) decreased with the decrease of DOM size fractions. The protein-like fractions of shrimp peptide DOM were high in each size fraction and mainly endogenous DOM, rich in organic matter from autochthonous sources and highly bioavailable. The size fractions of sheep manure DOM were greatly affected by human activities, however, the FI<1.4 for wheat straw biochar DOM in the larger size fraction (>100 kDa) indicated that its DOM in the larger size fraction was mainly exogenous with relatively low contribution from autochthonous production and microbial activities. In addition, although the HIX value of DOM of each size fraction of seaweed, sheep manure and shrimp peptide gradually decreased with the decrease of size fraction, except for the <1 kDa component of shrimp peptide DOM, the degree of humification was still high (HIX>10). While the HIX<4 of the small size fraction DOM of the wheat straw biochar indicated that the small size fraction DOM of the wheat straw biochar had a high content of hydrophobic components and a relatively low degree of humification. The fluorescence fractions and infrared spectra showed that the DOM of the four different organic fertilizers was dominated by humic substances and contained a large number of functional groups such as amino acid N―H, O―H and C―O.   【Conclusions】  Based on the size fractions distribution and spectral characteristics of organic fertilizers, DOM in seaweed, sheep manure, and shrimp peptide was mainly small size fraction, which was highly humified and has low protein content. The biostability of wheat straw biochar DOM was higher than other organic fertilizers, and the bioavailability was lower; therefore, the application of excessive biochar did not promote the microbial degradation and utilization of soil DOM; while the organic fertilizer of shrimp peptide source had the largest contribution of DOM protein-like fraction and high bioavailability. The application of shrimp peptide organic fertilizer may facilitate the degradation and utilization of soil DOM by microorganisms.