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

Meng Wu,Zhongpei Li,Chunyu Jiang,Mengya Song,Ming Liu

doi:10.1038/srep32858

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.

Highlights

The use of greenhouses in agriculture is expanding to 3.7 million hectares over the past two decades and plastic greenhouses occupied ~95% of the area covered by vegetable greenhouses[1]
The CHA/CFA ratio decreased from 1.22 in the 3-year cultivated soil to 0.89 in the 20-year cultivated soil and the CHA/CFA ratio of 10 and 20-year cultivated soil showed no significant difference with CK (P > 0.05)
Similar results were reported by Sun et al.[27], who found a decrease of 33% in the CHA/CFA ratio after 200 years cultivation for the black soil in the maize field

Summary

Introduction

The use of greenhouses in agriculture is expanding to 3.7 million hectares over the past two decades and plastic greenhouses occupied ~95% of the area covered by vegetable greenhouses[1]. Many farmers have shifted from conventional grain cropping to plastic greenhouse vegetable production (PGVP) systems. The structure change of organic matter in plastic greenhouses vegetable field is still not clear. Humic acid (HA) and fulvic acid (FA) are important components of organic matter in soil, interacting with plant growth and microorganism activity. HAs displayed many biological activities, there are no reports about the fungicide activity of humic substances against plant pathogenic fungi. The humic acid and fulvic acids extracted from greenhouse vegetable soils with different cultivation years were evaluated for their fungicidal activities against phytopathogenic fungi. The temporal variation of chemical structures of humic acids and fulvic acids and their relationship with fungicidal activities in plastic greenhouses vegetable field was investigated

Methods

Results

Conclusion