Drought responses of arbuscular mycorrhizal grapevines

Recent studies have focused on the effects of drought on arbuscular mycorrhizal (AM) vines, but many of the mechanisms of drought tolerance remain unclear. Gas exchange and nutritional strategies of drought tolerance in AM grapevines were investigated. One-year old grapevines, colonised with an AM fungus, were cultivated under glasshouse conditions, after which a 4 week drought period was induced. Shoot xylem water potentials were lower in all the drought stress plants. Although drought stress resulted in a decline in AM colonisation, the proline levels and biomass of AM plants were higher than the non-AM controls during the drought period. Despite AM plants having lower stomatal conductances and substomatal CO2 concentrations, similar photosynthetic rates were found between AM and non-AM plants under drought stress. As a result the water use efficiency was higher in the AM plants under drought stress. The photosynthetic response of AM plants during drought was associated with an increase in specific leaf mass and higher Rubisco activities and electron transport rates. These results indicate that drought stressed AM grapevines exhibited enhanced water use efficiencies by increasing proline accumulation and having higher investments of photosynthetic capacities to maintain similar CO2 fixation rates as non-AM grapevines.