PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Neotyphodium infection on growth and gas exchange of Arizona fescue under contrasting water availability.

Morse, Laura^*,1, Day, Thomas¹, Faeth, Stanley¹, ¹ Arizona State University, Tempe, Arizona

ABSTRACT- We assessed the influence of the endophytic fungi Neotyphodium on biomass production, growth and leaf gas-exchange and water relations of Arizona fescue (Festuca arizonica), by growing potted infected (E+) and uninfected (E-) plants under high or low water availability regimes. We measured growth, leaf net photosynthesis (P_n), chlorophyll fluorescence, conductance to water vapor (g_l) and water potential (), to provide explanations for differences in biomass production of E+ and E- plants. Under high water availability, E- plants produced more biomass and had greater relative growth rates (RGR) than E+ plants. Under low water availability, E+ plants produced more aboveground biomass and had greater RGR. Infected plants tended to have lower midday P_n and g_l in both water availability regimes. When more severe water stress was imposed in the low water availability treatment, E+ plants tended to have higher midday P_n and g_l. Infected plants also tended to have less negative leaf _g regardless of water availability regime. Lower g_l and transpirational losses of E+ plants probably conserved soil moisture, such that when a more severe water stress was subsequently imposed, E+ plants were able to maintain higher P_n and g_l than E- plants. Neotyphodium infection appears beneficial to Arizona fescue performance under low water availability, but detrimental under ample water availability, which may explain why these plants coexist in wild populations.

KEY WORDS: Festuca arizonica, fungal endophyte, drought, gas exchange