Gas exchange and chlorophyll fluorescence in symbiotic and non-symbiotic ryegrass under water stress

Abstract

The symbiotic association of endophyte fungus, Neotyphodium lolii, and ryegrass improves the ryegrass resistance to drought. This is shown by a 30 % increase in the number of suckers in infected plants (E+), compared to plants lacking endophyte (E-), and by a higher water potential in the E+ than E- plants: The E+ plants have higher stomatal conductance (g(s)), transpiration rate, net photosynthetic rate (P(N)), and photorespiratory electron transport rate than the E- plants. The maximal photochemical efficiency (F(v)/F(m)) and the actual photochemical efficiency (Φ(PS2)) are not affected by the endophyte fungus. The increase in P(N) of the E+ plants subjected to water stress was independent from internal CO2 concentration. An increased P(N) was observed in E+ plants also in optimal water supply. Hence the drought resistance of E+ plants results in increased g(s), P(N), and photorespiratory electron transport rate.