Mechanism of bare patch formation under Haloxylon ammodendron canopies and patch effects on soil microorganisms in the Gurbantunggut Desert, Northern China

Abstract Background and aims In the Gurbantunggut Desert, Haloxylon ammodendron and Syntrichia caninervis are often found at the base of the dunes. In these areas, bare patches usually form under the H. ammodendron canopy, but not under other shrub canopies. Methods We compared the soil chemical properties under H. ammodendron canopy inside the bare patches (UC) and of soil under moss crust outside of H. ammodendron canopy bare patches (UM), and used UHPLC-MS/MS to analyze soil metabolites and metagenomic sequencing to characterize the structure of soil microflora. Results A total of 951 metabolites were identified in the soil samples, and 518 differential metabolites were observed. The content of amides, such as oleamide, in UC soil was significantly higher than that in UM soil, suggesting that the amides may be the main allelochemicals inhibiting S. caninervis. The differences in soil chemical properties and metabolites impacted soil microorganisms, but the structure and function of microbial communities did not differ significantly. Conclusions The amides secreted by H. ammodendron roots create a concentration gradient under its canopy, with high concentrations inhibiting S. caninervis, causing changes in soil chemical factors inside and outside the bare patch. These changes affect the abundance of microbial species and relevant metabolic pathways. The differences in microbial communities and functions are caused by a combination of soil chemical properties and metabolites, rather than a direct effect of high levels of soil metabolites such as amides.