Abstract
The complex composition and interaction of root-associated microbes are critical to plant health and performance. In this study, we presented a detailed characterization of three rhizocompartment (rhizosphere, rhizoplane, and root) microbiomes of Achyranthes bidentata under different years of consecutive monoculture by deep sequencing in order to determine keystone microorganisms via co-occurrence network analysis. The network analysis showed that multiple consecutive monoculture (MCM, represented 5Y and 10Y) soils generated some distinct beneficial bacterial taxa such as Bacillus, Fictibacillus, Bradyrhizobium, Shinella, and Herbaspirillum. For fungi, Mortierella substituted for Fusarium in occupying an important position in different rhizocompartments under A. bidentate monoculture. Quantitative PCR analysis confirmed a significant increase in Bacillus, Pseudomonas, and Burkholderia spp. The results of the inoculation assay showed that addition of beneficial bacteria Bacillus subtilis 74 and Bacillus halodurans 75 significantly increased the root length and fresh weight of A. bidentata. Furthermore, three types of phytosterones, as the main allochemicals, were identified both in the rhizosphere soil and in culture medium under sterile conditions by LC-MS/MS. When looking at in vitro interactions, it was found that phytosterones displayed a positive interaction with dominant beneficial species (Bacillus amyloliquefaciens 4 and B. halodurans 75) and had a negative effect on the presence of the pathogenic fungi Fusarium solani and Fusarium oxysporum. Overall, this study demonstrated that consecutive monoculture of A. bidentata can alter the bacterial and fungal community by secreting root exudates, leading to recruitment of beneficial microbes and replacement of plant-specific pathogenic fungi with plant beneficial fungi.
Highlights
Chinese medicine resources are a key point for human disease treatment
The results revealed that compared to the less continuously planted plot (1Y and 3-year consecutive monoculture (3Y)), the contents of total phosphorus (TP) and available nitrogen (AN) in rhizospheric soils were significantly (p < 0.05) higher in the multiple continuous monoculture soil systems (5Y and 10-year consecutive monoculture (10Y))
It can be clearly seen that both plant and soil environment provided an ideal habitat for some microorganisms, and these species had a great impact on plant productivity (Van der Heijden et al, 2008; Schlaeppi and Bulgarelli, 2015)
Summary
Chinese medicine resources are a key point for human disease treatment. Rehmannia glutinosa, Radix pseudostellariae, and Achyranthes bidentata are perennial herbaceous plants that are highly valued in traditional Chinese medicine with a surging market demand (Li et al, 2015; Sun et al, 2015; Wu et al, 2017). Many medicinal plant species, such as R. glutinosa and R. pseudostellariae, are grown under a continuous cropping system in a geo-authentic production zone because the synthesis of bioactive constituents of certain Chinese medicinal plants is closely correlated to ecological factors (Zhang et al, 2010). This system can have a detrimental effect on soil quality leading to a significant decline in plant biomass and vigor as well as increasing occurrence of plant pests (Wu et al, 2015, 2019). There is an urgent need to fully understand the complex reasons why different crops respond differently to continuous cropping in the managed farming system
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