Host selection has stronger impact on leaf microbiome assembly compared to land-management practices
Plant microbiome contribute directly to plant health and productivity but mechanisms that underpin plant microbiome assembly in different compartments (e.g. root, leaf) are not fully understood. Identifying environmental and management factors that affect plant microbiome assembly is important to advance understanding of fundamental ecological processes and harnessing microbiome for improved primary productivity and environmental sustainability. Irrigation and fertilization are two common management practices in Australian tree plantations, but little is known about the effects of these treatments on soil, plant host, and their microbiome. Here, we investigated the impact of a decade long irrigation, fertilization, and their combined application, on soil, plant traits and microbiome of a Eucalyptus saligna plantation at the Hawkesbury Forest Experiment, Western Sydney University, Richmond, NSW. Microbial profiling of bulk soil, rhizosphere, root, and leaves was performed using amplicon sequencing 16S rDNA and ITS markers for bacteria and fungi, respectively, along with measurements of soil properties and plant traits. The results indicated that both management practices affected soil properties and soil and root microbiome significantly. Irrigation increased but fertilizer treatment reduced microbial alpha diversity. However, neither irrigation nor fertilizer treatment significantly impacted the leaf microbiome. Our findings imply that management practices impact soil edaphic factors, which in turn influence the below ground microbiome (soil and root). In addition, the leaf microbiome was distinct from soil and root microbiome, and a source tracker analysis suggested root and bulk soils only contributed to 53% and 10% OTUs of the leaf bacterial community, suggesting strong and sequential host selection of the leaf microbiome. In addition, management practices had limited impact on leaf traits and, consequently, the leaf microbiome maintained its distinct composition. These findings provide mechanistic evidence for ecological processes that drive plant microbiome assembly and indicate that host selection plays a more important role than management practices on leaf microbiome assembly.