Poster: Plant-symbiont interactions
Abs #
593: Endophytic Tall Fescue Grasses Show Greater Stomatal Responses To Changes in CO2 Concentrations in Intact Leaves
Festuca arundinaceae (Tall fescue) has a symbiotic relationship with an endophyte, Neotyphodium coenophialum. Past experiments have shown that the presence of the fungus in the stem and leaf sheaths increases the drought tolerance of the grass because stomata close earlier under water stress conditions. We subjected endophytic and non-endophytic tall fescues to two water (high and low) and two nutrient treatments (high and low) for 12 weeks. Using a LiCor 6400, we monitored gas exchange variables by generating A:Ci curves at 8 and 12 weeks after germinination to determine carboxylation capacities at different availabilities of nutrients and water availability. We found that rates of stomatal conductance and transpiration were significantly lower in the endophytic plants when water and nutrients were limiting at 12 weeks. Although there were no differences in rates of photosynthesis at ambient CO2 concentration (400 ppm) and A:Ci parameters among the endophytic versus non-endophytic grasses in each treatment, the mean rates of change in stomatal conductance were greater in endophytic grasses when nutrients and water were limiting. The mean rate of reduction in stomatal conductance was four times greater when CO2 levels increased between 600 and 1000 ppm and water vapor mole fractions were kept constant in the chamber. When CO2 levels decreased between 400 and 50 ppm, the mean rate of increase in stomatal conductance was double that of the non-endophytic grasses. This suggests that stomata are more receptive to CO2-mediated stomatal regulatory signaling in the presence of the fungus. One possibility is that the fungus may produce ABA that is directed to the guard cells when the fungus is present in the stem and leaf sheaths.
