Neotyphodium coenophialum-endophyte infection affects the ability of tall fescue to use sparingly available phosphorus

Neotyphodium coenophialum, (Morgan-Jones & Gams) Glenn, Bacon & Hanlin, inf ected tall fescue (Festuca arundinacea Schreb.) plants perform better than non-infected isolines on phosphorus (P)-deficient soils. Our objective was to characterize growth and P uptake dynamics of tall fescue in response to endophyte infection and P source at low P availability in soil. Two tall fe scue genotypes (DN2 and DN4) infected with their naturally occurring N. coe nophialum strains (E+), and in noninfected (E-) forms were grown in Lily so il (fine loamy siliceous, mesic Typic Hapludult) in a greenhouse for 20 wee ks. Three soil P treatments were imposed: no P supplied (control) and P sup plied as commercial fertilizer (PF) or as phosphate rock (PR) at the level of 25 mg P kg(-1) soil. Interaction of tall fescue genotype and endophyte s tatus had a significant influence on mineral element uptake suggesting high specificity of endophyte-tall fescue associations. Endophyte infection did not affect root dry matter (DM) when no P was supplied but shoot DM was re duced by 20%. More biomass was produced and greater P uptake rate occurred in PR than PF treatment. Root DM was greater in E+ DN4 than E-DN4 when supp lied with either PF or PR. In contrast, endophyte infection did not affect root DM of DN2, regardless of P source. Relative growth rate (RGR) of E+ pl ants grown with PR was 16% greater than that of E- plants. Endophyte infect ion did not improve growth or P uptake in PF treatment. When PR was supplie d, P uptake rate was 24% greater in E+ DN2 than E- DN2, but endophyte infec tion did not benefit DN4. Phosphorus-use efficiency was 6% less in E+ DN2 b ut 16% greater in E+ DN4 compared to E- plants, regardless of P source. Roo t exudates of E+ DN2, but not E+ DN4 solubilized more P from PR than those of E- plants. The correlation between root RGR and P uptake rate was relati vely high for E- plants (r=0.76), but low for E+ plants (r=0.27) grown with PR. Results suggest that P uptake by E+ tall fescue might rely on mechanis ms other than an increase in root biomass (surface area). Endophyte infecti on modified tall fescue responses to P source. This phenomenon was associat ed with modes of P acquisition which included enhanced activity of root exu dates in releasing P from PR in E+ plants (DN2), and increased root biomass (DN4). The dominant means of P acquisition may be determined by a specific association of endophyte and tall fescue genomes. Endophyte-tall fescue as sociation plasticity contributes to widespread success of symbiotic in marg inal resource conditions.