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

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