Effects of phenolic acids from ginseng rhizosphere on soil fungi structure, richness and diversity in consecutive monoculturing of ginseng

Abstract

Ginseng yield and quality are seriously compromised by consecutive monoculturing in northeastern China. The imbalance of soil fungi communities and autotoxicity of ginseng are the major factors in consecutive monoculturing ginseng crops. Soil fungal communities were identified using Illumina MiSeq sequencing, applied to soils that consecutively cultured ginseng (CCG) for six years and new forest soil (NFS), or receiving application of phenolic acids (PAs). The CCG field received five treatments with five different phenolic acids, including gallic acid (GA), salicylic acid (SA), 3-phenylpropionic acid (3-PA), benzoic acid (BA) and cinnamic acid (CA), which were detected from ginseng rhizosphere in consecutive cropping soil. Fungal richness, fungi diversity, community composition, relative taxon abundances, root rot disease, and growth rate were compared among the different treatments. 579 fungal operational taxonomic units at 97% ITS sequence identity were found among 201,617 sequence reads derived from 18 separate soil samples. Members of the phylum Ascomycota dominated the soil fungal communities, and putative pathogens, such as Fusarium, Gibberella and Nectriaceae_unclassified which may include the abundant sexual morph of Cylindrocarpon destructans, showed higher relative abundances in the CCG fields. Compared to the CCG and NFS fields, PAs (except CA) enhanced the fungi richness and decreased fungi diversity. Cluster analysis indicated that the PAs (except CA) changed the fungi structure in a uniform way. PAs stimulate root rot disease and enhance disease severity, restricting plant growth. The results suggest that the PAs (except CA) may enhance the fungi richness, decrease the fungi diversity and changed the fungi structure to increase fungal pathogen loads, which could explain the declined yield and quality of ginseng in consecutively monocultured ginseng crops.

Keywords: Next generation deep sequencing; Obstacle of ginseng consecutive monoculturing; Phenolic acids; Soil fungi communities.

Fig. 1

Rarefaction curves at the 97% similarity level. Rarefaction curves showing the relationship between sampling intensity and the number of recovered OTUs from the different seven treatments. Sequences of the nuclear internal transcribed spacer region were grouped at 97% sequence identity.

Fig. 2

Numerically dominant clades in the fungal communities at the phylum level. Relative abundances of the main fungal phylums in the soil of the seven treatments. The relative abundances of those fungal DNA sequences are shown that could be ascribed to a phylum of fungi, except for “Others”, which comprises all the rare remaining phylums.

Fig. 3

Numerically dominant genus in the fungal communities at the class level. Relative abundances of the main fungal genus in the soil of the seven treatments. The relative abundances of those fungal DNA sequences are shown that could be ascribed to a genus of fungi, except for “Others”, which comprises all the rare remaining genus.

Fig. 4

Hierarchical clustering analysis in the fungal communities at the genus level.

Fig. 5

Root rot disease indexes of seven treatments. Bars above the histogram represent the standard error of three replicates. Letters above the bars indicate a significant difference according to Duncan’s multiple range test at P < 0.05 level.

Fig. 6

Growth rate of root weight of seven treatments. Bars above the histogram represent the standard error of five replicates. Letters above the bars indicate a significant difference according to Duncan’s multiple range test at P < 0.05 level.