This study evaluates the interaction effects on corn (Zea mays L.) growth between intact humic substances (HS) extracted in an alkaline medium from three different origins (an Organosol [HS-Org], an Andisol [HS-And], and vermicompost [HS-Vc]) and the arbuscular mycorrhizal fungus (AMF) Dentiscutata heterogama. The HS were characterized by spectroscopic techniques, and different biochemical, morphological, nutritional, and AMF colonization parameters were evaluated in corn plants. The experiment was conducted in a greenhouse, and low-fertility soils sterilized after solarization were used as the substrate. Hybrid corn BR-3025 was planted, and the HS concentrations used were 5, 10, and 20 mg carbon L −1 for HS-And, HS-Vc, and HS-Org, respectively, applied 15, 25, and 45 d after emergence close to the roots. The results show that HS application and D. heterogama inoculation significantly stimulated the biomass in relation to the treatments without AMF. Carbohydrate and protein content were stimulated by HS-AMF interaction. A higher leaf content of nutrients was observed in the AMF-and HS-inoculated plants. The HS-Vc application and AMF inoculation resulted in intense stimulation, which was confirmed with a high mycorrhizal efficiency. The spore density and glomalin content were also stimulated by the three different HS applications independently of their source. The HS-Vc has intermediate structural chemical characteristics in terms of polarity and aromaticity compared with HS-Org and HS-And. The HS-Vc more strongly stimulated the plant physiological parameters when combined with the AMF inoculation. These results may indicate that the HS formed in soil and characterized by structures that are more balanced may function more effectively.
The understanding of humic substances (HS) chemistry in soil science faces new challenges at present. Theories alternative to humification (HS formation process) have been presented to scientific community propagating uncertainty about the existence of these compounds as a structural entity located in the soil. In this review, we aim to show in a compressible manner that HS have a structural pattern independent of its origin, which allows us the characterization by means of techniques common to other groups of compounds ( 13 C NMR CP/MAS). These characteristics (C-aliphatic, Caromatic, carboxyl, carbonyl) allow the obtaining and quantification of HS properties (aromaticity, aliphaticity, hydrophobicity, recalcitrance) that define different functions in the soil (plant bioactivity). The preservation of the structureproperty-function relationship of HS qualifies them as a chemical compounds groups that are formed in the soil and are widely distributed in nature. The relevance of the supramolecularity concept to explain chemical and organizational characteristics of the humic structure, as well as, the use of spectroscopic techniques combined with chemometrics to understand the complex behavior of HS and its various functions is highlighted in this review. ResumoO entendimento da química das substâncias húmicas (SHs) na ciência do solo enfrenta hoje novos desafios. Teorias alternativas à humificação (processo de formação das SH) têm sido apresentadas à comunidade científica gerando questionamentos sobre a existência destes compostos como uma entidade estrutural presente no solo. Esta revisão tem como objetivo mostrar de forma compreensível que as SHs possuem um padrão estrutural independente da fonte de origem, que permite a caracterização por meio de técnicas comuns a outros grupos de compostos ( 13 C NMR CP/MAS). As características que as SHs apresentam (C-alifáticos, C-aromáticos, carboxilas, carbonilas) permitem a obtenção e quantificação de propriedades (aromaticidade, alifaticidade, hidrofobicidade, recalcitrância) que definem as diferentes funções que as mesmas exercem no solo (bioatividade em plantas). A preservação da relação estrutura-propriedade-função das SHs as qualifica como compostos químicos que são formados no solo e que estão amplamente distribuídos na natureza. Destaca-se nesta revisão a importância do conceito de supramolecularidade para explicar as características químicas e organizacionais da estrutura húmica e o uso de técnicas espectroscópicas aliadas à quimiometria para entender o comportamento complexo das SHs e suas diversas funções.Palavras-chave: Ácidos húmicos; espectroscopia; quimiometria; estresse oxidativo.
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