Implications of Microbial Community Composition for Sparingly-Soluble Phosphates Uptake By Fungal Endophyte Infected Tall Fescue in Acidic Soil.

Fungal endophyte infection in tall fescue is thought to improve phosphorus acquisition from soils.  An experiment was carried out to test if fungal endophyte strain influenced tall fescue’s ability to access P from four P sources varying in solubility. In a greenhouse study, novel endophyte infected (AR542E+ or AR584E+), common toxic endophyte infected (CTE+), or endophyte-free tall fescues were grown for 90 days in an acidic (pH5.50), low-P soil or in soils spiked with 30 mg·P·kg^-1 of potassium dihydrogen phosphate (KH₂PO₄, K-Ps), iron phosphate (FePO₄, Fe-Ps), aluminum phosphate (AlPO₄, Al-Ps), or tricalcium phosphate (Ca₃(PO₄)₂, Ca-Ps), respectively. At the end of the study plant biomass, P uptake, rhizosphere microbial community structure, and potential acid phosphatase activity (AcPase) were measured. P form strongly influenced tall fescue biomass production and P acquisition. P uptake and vegetative biomass production was similar for plants grown with Al-Ps, Ca-Ps and K-Ps but greater than those plants grown in control soils.  Fe-Ps proved to be the least available P form evidenced by the smallest biomass production, lowest P content and typical P deficiency symptoms. Overall, infection with AR542E+ resulted in significantly less shoot biomass than E+ and E- varieties with no influence of endophyte on root biomass or P acquisition.  P form was the strongest factor affecting total microbial biomass, microbial community structure and specific PLFA biomarker groups (G+, G-, AM fungi) in rhizosphere soils. AM fungi (16:1ω5c) was effective at predicting variations in P uptake and tall fescue biomass. There was a significant negative relationship between AcPase and P availability the former of which was strongly influenced by the interaction of endophyte × P form; although this relationship was inconsistent. Our results provide little evidence for enhanced P acquisition by tall fescue due to endophyte infection.