The advantages of endophyte-infected over uninfected tall fescue in the growth and pathogen resistance are counteracted by elevated CO2

Abstract

Atmospheric CO₂ concentrations are predicted to double within the next century. Despite this trend, the extent and mechanisms through which elevated CO₂ affects grass-endophyte symbionts remain uncertain. In the present study, the growth, chemical composition and pathogen resistance of endophyte-infected (E+) and uninfected (E-) tall fescue were compared under elevated CO₂ conditions. The results showed that the effect of endophyte infection on the growth of tall fescue was significantly affected by elevated CO₂. Significant advantage of E+ over E- tall fescue in tiller number, maximum net photosynthetic rate and shoot biomass occurred only under ambient CO₂. With CO₂ concentration elevated, the beneficial effect of endophyte infection on the growth disappeared. Similarly, endophyte infection reduced lesion number and spore concentration of Curvularia lunata only under ambient CO₂. These results suggest that the beneficial effect of endophyte infection on the growth and pathogen resistance of tall fescue could be counteracted by elevated CO_2. An explanation for the counteraction may be found in a change in photosynthesis and nutritive quality of leaf tissue.

Figure 1

Comparison of tiller number of endophyte-infected (E+) or uninfected (E−) Festuca arundinacea under elevated CO₂ (EC) and ambient CO₂ (AC) conditions. *Meant significant difference at 0.05 level.

Figure 2

Comparison of maximum photosynthetic rate and shoot biomass of endophyte-infected (E+) or uninfected (E−) Festuca arundinacea under different CO₂ and nitrogen levels. *Meant significant difference at 0.05 level.

Figure 3

Leaf N concentration of endophyte-infected (E+) or uninfected (E−) Festuca arundinacea under different CO₂ and nitrogen levels (a). Leaf C:N ratio of Festuca arundinacea under different endophyte (b) and CO₂ treatments (c). *Meant significant difference at 0.05 level.

Figure 4

Lesion number (a) and pathogen spore concentration (b) of endophyte-infected (E+) or uninfected (E−) Festuca arundinacea under elevated CO₂ (EC) and ambient CO₂ (AC) treatments.*Meant significant difference at 0.05 level.

Figure 5

Soluble sugar concentration of Festuca arundinacea under different endophyte (a) and CO₂ treatments (b). *Meant significant difference at 0.05 level.

Figure 6

Loadings for each individual amino acid of Festuca arundinacea onto the first four rotated factors (RF). The individual amino acids loading heavily either positively (loading ≥ +0.5) or negatively (loading ≤ −0.5) are highlighted in black.

Figure 7

Mean response of rotated factors (RF1–4, A,C,E,G) and the standardized univariate response (B,D,F,H) of individual amino acids in Festuca arundinacea under different endophyte status (E+, endophyte-infected; E−, uninfected), CO₂ concentration (EC, 800 ppm; AC, 400 ppm), and pathogen inoculation (P+, inoculated by Curvularia lunata; P−, uninoculated control). *Meant significant difference at 0.05 level.

Figure 8

Lignin concentration of endophyte-infected (E+) or uninfected (E−) Festuca arundinacea under different CO₂ concentration (EC, 800 ppm; AC, 400 ppm), and pathogen inoculation (P+, inoculated by Curvularia lunata; P−, uninoculated control). *Meant significant difference at 0.05 level.