EFFECTS OF SEX AND MYCORRHIZAL FUNGI ON GAS EXCHANGE IN THE DIOECIOUS SALT MARSH GRASS DISTICHLIS SPICATA

Premise of research. In dioecious plant species, males and females often differ in physiology, and mycorrhizal fungal relationships are likely to influence these differences. However, few data are available on the potential role of mycorrhizal fungi in altering sex-specific physiology and population sex ratios of dioecious plant species. Methodology. In this study, we measured leaf gas exchange in a multifactorial greenhouse experiment with and without mycorrhizal fungal additions and under field conditions in Distichlis spicata, a dioecious salt marsh grass, displaying extreme spatial sex ratio variation. Pivotal results. We found a significant interaction between gas exchange, plant sex, and mycorrhizal fungal infection. Specifically, females but not males had significantly lower transpiration rates and higher water use efficiency (WUE) in treatments with increased mycorrhizal fungi. Additionally, field data showed similar WU between plants at female-majority sites and male-majority sites, despite significantly lower rates of net assimilation and stomatal conductance in plants at female-majority sites. Conclusions. Our results suggest that the higher WUE associated with increased mycorrhizal fungi female D. spicata plants may be an important physiological attribute enabling female success in the higher-stress salt-water environment contributing to the spatial segregation of the sexes observed in this dioecious species.