The Effects of Host Plant Genotype and Environmental Conditions on Fungal Community Composition and Phosphorus Solubilization in Willow Short Rotation Coppice

Abstract

Phosphorus (P) is an essential plant nutrient. Low availability of P in soil is mainly caused by high content of Fe₂O₃ in the clay fraction that binds to P making it unavailable. Beneficial microbes, such as P solubilizing microorganisms can increase the available P in soil and improve plant growth and productivity. In this study, we evaluated the effects of environmental conditions (climate, soil parameters), plant genotype, and level of plant association (rhizosphere or endophytic root organism) on the abundance and diversity of phosphorus solubilizing microorganisms in a <i>Salix</i> production system. We hypothesized that a lower number of endophytic fungi may possess the ability to solubilize P compared to the number of rhizosphere fungi with the same ability. We also expect that the plant genotype and the experimental site with its environmental conditions will influence fungal diversity. Two <i>Salix</i> genotypes grown in pure and mixed cultures were investigated for their fungal microbiome community and diversity in the rhizosphere and endosphere during two growing seasons. We found that the rhizosphere fungal community was more diverse. A general dominance of Ascomycota (<i>Dothideomycetes</i>) and Basidiomycota (<i>Tremellomycetes</i>) was observed. The classes <i>Agaricomycetes</i> and <i>Pezizomycetes</i> were more frequent in the endosphere, while <i>Tremellomycetes</i> and <i>Mortierellomycetes</i> were more abundant in the rhizosphere. Plot-specific soil properties (pH, total organic carbon, and nitrogen) significantly influenced the fungal community structure. Among the culturable fungal diversities, 10 strains of phosphate solubilizing fungi (PSFs) from roots and 12 strains from rhizosphere soil were identified using selective media supplemented with di-calcium and tri-calcium phosphates. The fungal density and the number of PSF were much higher in the rhizosphere than in the endosphere. <i>Penicillium</i> was the dominant genus of PSF isolated from both sites; other less frequent genera of PSFs were <i>Alternaria, Cladosporium</i>, and <i>Clonostachys</i>. Overall the main factors controlling the fungal communities (endophytic vs. rhizosphere fungi) were the soil properties and level of plant association, while no significant influence of growing season was observed. Differences between <i>Salix</i> genotypes were observed for culturable fungal diversity, while in metagenomic data analysis, only the class <i>Dothideomycetes</i> showed a significant effect from the plant genotype.