Fungicidal activities of soil humic/fulvic acids as related to their chemical structures in greenhouse vegetable fields with cultivation chronosequence

Abstract

In the background of rapid expansion of plastic greenhouse vegetable production in China, many environmental risks have emerged in recent years. In this study, the soils with a chronosequence in greenhouse vegetable fields were collected and the soil humic acids (HAs) and fluvic acids (FAs) were extracted and purified. The soil HAs and FAs were found to show inhibition activities against phytopathogenic fungi for the first time. Fourier transform infrared spectroscopy was performed to investigate the chemical structures of HAs and FAs. The variation of relative peak areas indicated the chemical structure of HAs become more complex and stable under continuous cultivation. The PCA analysis showed HAs and FAs could be distinctly separated from each other and cultivation years mainly determined the variation. Mantel test and RDA analysis indicated the active components (aliphatic peaks for HAs and COOH, OH peaks for FAs) had positive correlation with the inhibition rates of HAs and FAs against phytopathogenic fungi. According to our research, the active fungicidal components in soil HAs and FAs decreased along with the extension of cultivation years, which made the soil suffer more risk to phytopathogenic fugi. So we believe continuous cultivation too many years in PGVP systems is inadvisable.

Isolation, Characterization, and Environmental Application of Bio-Based Materials as Auxiliaries in Photocatalytic Processes

“…1130 cm −1 attributable to C-O stretching vibration modes due to alcoholic and ether functionalities ( Figure 1, black star). The interpretation of spectra was according to the literature [55,56]. Thus, BBS-HA appeared to be characterized by a higher aromatic character, in agreement with SUVA findings, and by the incorporation of proteinaceous residues.…”

“…Thus, BBS-HA appeared to be characterized by a higher aromatic character, in agreement with SUVA findings, and by the incorporation of proteinaceous residues. As expected by the extraction method, the BBS-FA fraction has a higher amount of carboxyl groups [55,56]. Figure 1, white circles) [55].…”

“…As expected by the extraction method, the BBS-FA fraction has a higher amount of carboxyl groups [55,56]. Figure 1, white circles) [55]. Interestingly, the BBS-HA presents also a shoulder at ca.…”

“…1650-1630 cm −1 attributable to aromatic C=C skeletal vibrations ( Figure 1, black squares), more pronounced in BBS-HA than in BBS-FA; (v) a broad band at 1420-1410 cm −1 assigned to both O-H deformation and C-O stretching modes of phenolic moieties ( Figure 1, red circles); (vi) an intense band at 1230-1220 cm −1 due to both C-O stretching and O-H deformation modes of COOH groups ( Figure 1, red circles). The band in the 1040-1030 cm −1 range is attributed to C-O stretching of polysaccharides and polysaccharide-like impurities (i.e., residues of the non-humic fraction, Figure 1, white circles) [55]. Interestingly, the BBS-HA presents also a shoulder at ca.…”

“…Thus, BBS-HA appeared to be characterized by a higher aromatic character, in agreement with SUVA findings, and by the incorporation of proteinaceous residues. As expected by the extraction method, the BBS-FA fraction has a higher amount of carboxyl groups [55,56]. 13 C solid-state nuclear magnetic resonance (NMR) spectroscopy offers the possibility of direct chemical characterization of organic materials in terms of content of different functional groups [57][58][59].…”