Arbuscular mycorrhizal fungus modulates vulnerability to xylem cavitation of populus × canadensis 'neva' under drought stress

To avoid xylem cavitation, plants adopt water manage behaviors from water-conserving to risk-taking to regulate stomatal conductance under drought stress, and the behaviors may shift due to sink demand. Arbuscular mycorrhizal (AM) fungi form symbioses with plants, generate sink demand and promote stomatal conductance, which would increase water loss and vulnerability to xylem cavitation. However, the effect of AM fungi on plant water manage behavior and vulnerability to xylem cavitation was rarely reported. The impact of an AM fungus (Rhizophagus irregularis) on growth, gas exchange, photosynthesis, and vulnerability to xylem cavitation of Populus × canadensis "Neva" was evaluated under three water status (70%-75%, 50%-55%, 30%-35% of field capacity). After 250 days, R. irregularis colonized more than 70% roots, increased biomass accumulation, improved gas exchange, photosynthesis, leaf relative water content, and specific leaf area of poplar plants. Drought stress limited R. irregularis colonization rate, plant biomass accumulation, and parameters of gas exchange and photosynthesis. Inoculation of R. irregularis seemingly shifted water manage behavior from water-conserving toward risk-taking and modulated the vulnerability to xylem cavitation. Results of current study suggested that plant genes involved in water management and traits for xylem cavitation may be regulated by AM symbiosis and require further study. (author)