Mycorrhizal symbiosis and water condition affect ozone sensitivity of Medicago sativa L. by mediating stomatal conductance

Abstract

Ground level ozone (O 3 ) pollution is a common environmental stress for plants in many regions of the world, while plant O 3 sensitivity is largely influenced by plant water status. Arbuscular mycorrhizal (AM) fungi can form symbiosis with most terrestrial plants and play important role in plant resistance to various environmental stresses. However, how AM symbiosis and water conditions affect plant O 3 sensitivity and the underlying mechanism remain unclear. In this study, alfalfa ( Medicago sativa L.) was used as test plant, and the effects of AM inoculation and water conditions on plant growth and stress physiology under O 3 enrichment were investigated. The results showed that O 3 enrichment inhibited plant growth and caused visible injury on plant leaves. Water deficiency also caused significant decrease in plant biomass, while AM symbiosis promoted plant growth regardless of water condition and O 3 enrichment. In general, water deficiency decreased while AM symbiosis increased plant O 3 sensitivity. Nevertheless, under severe water deficiency, AM inoculation promoted plant growth without increasing plant O 3 sensitivity. Water deficiency increased antioxidant enzyme activities and decreased stomatal conductance, while AM symbiosis increased both antioxidant enzyme activities and stomatal conductance. A significant negative correlation between stomatal conductance and O 3 effect on plant total biomass supported that both water condition and AM symbiosis affect O 3 sensitivity mainly through mediating stomatal conductance. However, AM symbiosis and water condition may differ in regulation mechanisms for stomatal conductance, as AM colonization significantly increased stomatal density, while water deficiency decreased stomatal aperture. Our study suggested that AM inoculation in combination with proper water management could largely mitigate the negative effects of O 3 on plants. • Water deficiency decreases stomatal conductance and plant O 3 sensitivity. • AM symbiosis increases stomatal conductance and plant O 3 sensitivity. • AM fungi and water condition affect stomatal conductance through different pathways. • AM inoculation combined with water management could mitigate negative effects of O 3 on plants.