School of Agriculture and Food Sciences, The University of Queensland
Plants activate salicylic acid (SA) signalling to combat biotrophic pathogens among other functions. In the present study, we examined the effect of artificially elevated SA signalling on the microbial communities in the wheat (Triticum spp.) rhizosphere. We tested the hypothesis that the activation of SA signalling defence pathway alters the composition and functional diversity of rhizosphere microbial communities. Wheat was grown in two agricultural soils of different soil types (Solonetz and Calcisol), which have been used for continuous wheat cropping for many years. SA was exogenously applied to 10 day-old wheat seedlings, and rhizosphere soils were collected 72 h after SA application. Phylogenetic marker gene sequencing (16S rRNA gene) was used to characterise the bacterial and archaeal diversity. ChitinaseA and nitrogen (N) cycling genes including nifH, arch-amoA, amoA, nosZ and narG were quantified to determine the potential changes in functional diversity of the wheat rhizosphere. SA signalling marginally changed the composition of rhizosphere microbial communities in Solonetz (P=0.093) but not in Calcisol (P=0.31). In particular, SA signalling increased two Lysobacter and Pseudomonas species abundance that are involved in biocontrol in Solonetz. It also triggered a significant decrease in the archaea member Candidatus nitrososphaera in Solonetz but not in Calcisol. In addition, the amoA-arch gene was less expressed in the rhizosphere after SA pathway activation in Solonetz, as revealed by qPCR. nifH, amoA and nosZ were significantly supressed at 72 h after the activation of SA signalling in Solonetz soil. Our results suggest that SA signalling alters the wheat rhizosphere microbiome and led to a decrease of bacterial components involved in N cycling in a soil dependent way.