Structure–Property–Function Relationship of Humic Substances in Modulating the Root Growth of Plants: A Review

Abstract

The structural identity of humic substances (HS) in the soil is a highly debated issue in the soil sciences. Although the complexity and structural characteristics that determine the functions of HS justify their further study, there is enough scientific evidence explaining the presence of these compounds as a group of structures that are formed by humification and have unique chemical characteristics. This review presents scientific information that follows the structure-property-function relationship with the objective of better explaining the nature of HS. On the basis of the spectroscopic characterization of a number of humic acids, together with the use of chemometric techniques, it is shown that, although the sources of origin are different, HS have a unique structural pattern that is different from that of any other group of soil compounds. From this structural pattern, it is possible to understand how fragments with greater lability in HS can reach root surfaces and interact with the cell membrane, regulate oxidative metabolism, and stimulate root growth in plants. Lability and recalcitrance are properties arising from the characteristics and suprastructural organization of HS and can define the type and intensity of the bioactivity of HS in plants. In this review, we demonstrate that there are methods for studying HS by which a deeper understanding of the functions of these substances on the basis of their chemical properties is possible. Therefore, the understanding of this complex system allows the connection of the scientific elements that justify the existence of these compounds in the soil.

Morfofisiologia Do Capim Mombaça Em Função De Fertilizantes Nitrogenados Estabilizados

“…As substâncias húmicas são parte da matéria orgânica humificada, que se divide em três frações orgânicas: humina, ácidos húmicos (AH) e ácidos fúlvicos (AF) (MENDONÇA; MATOS, 2005). Vários estudos relatam que as duas últimas frações possuem bioatividade em plantas que estão relacionadas com as características estruturais (PERMINOVA et al, 2019), e são influenciadas pelo material de origem e tempo de transformação (BETTONI et al, 2016;CANELLAS;SANTOS, 2005;GARCÍA et al, 2019;OLIVARES et al, 2017) Os estudos mostram que as substâncias húmicas afetam o metabolismo (DU JARDIN, 2015) e a fisiologia das plantas (GARCÍA et al, 2019) Tabela 2. Resumo da análise de variância com os valores dos quadrados médios e nível de significância para as variáveis, altura de plantas (ALT), número de perfilhos (PERF), massa fresca (MFPA) e seca da parte aérea (MSPA), relação da massa fresca com a massa seca (RFS), massa de perfilhos (MPER), área foliar (AFo) e índice de clorofila Falker (ICF), do capim Marandu sob a aplicação foliar de doses de ácidos húmicos e fúlvicos.…”

“…O aumento no acúmulo de biomassa está associado a uns dos efeitos bem descritos das SHs, que atuam de forma semelhante ao fi tohormônio auxina (DU JARDIN, 2015) promovendo alterações morfoanatómicas e bioquímicas que resultam na intensifi cação da formação de raízes laterais (AMORIM et al, 2015) e pêlos radiculares (GARCÍA et al, 2019) que maximizam a superfície de contato da raiz, favorecendo o transporte de íons, absorção de água e nutrientes (TAIZ et al, 2017).…”

“…Estes efeitos são típicos de aplicações exógenas de hormônios de plantas, que acabam provocando um desequilíbrio fisiológico e bioquímico, uma vez que os hormônios são os principais mensageiros que modulam esses processos (BETTONI et al, 2016;GARCÍA et al, 2019;OLIVARES et al, 2017;SHAH et al, 2018).…”

Current Understanding of the Use of Alkaline Extractions of Soils to Investigate Soil Organic Matter and Environmental Processes

“…García et al (2019) provide a broad review of the recent spectroscopic and functional analysis of humic substances extracted from tropical soils that suggest that the characteristic spectral signatures indicate that they are composed of unique structural and chemical moieties. Furthermore, they present results on humic substance treatments indicating that these are responsible for the phenotypic responses observed in plant studies.…”

“…Although methodologies reviewed for structural characterization are limited to solid‐state 13 C NMR, the ability of microscopy and enzyme tags to spatially associate these substances on plant tissues are also reviewed. Additionally, García et al (2019) discuss various chemical processes, such as regulation of reactive oxygen species, stimulation of enzymatic activity, and quenching of stress signaling in plants that result in enhanced plant growth. Their work puts a specific emphasis on root system architecture and emergence of lateral roots, as well as impacts on gene regulation of the observed metabolic response.…”