Impact of water stress on plant water relations, growth and mycorhization of Acacia tortilis ssp. raddiana: Interactions of the stress severity and duration, and the AM fungal species.

Mycorrhizae are commonly reported to improve drought resistance of the host plant. Investigating factors controlling the plant-resistance strategy to water stress can however lead to a suitable management of mycorrhizal plants under drought. Here, we focused on the impact of interactions of the AM fungal species and water stress severity and duration on mycorrhizal Acacia tortilis ssp. raddiana in terms of plant growth, mycorhization and water relations. We used three Glomus species, which were G. mosseae, G. deserticola and G. intraradices. We applied three watering regimes that were maximum water holding non-stress regime, mild-severe water stress and severe water stress. Measurements were performed at four stage durations named pre-drought (one day before applying water stress), early-drought (30 days after applying water stress), mid-drought (60 days after applying water stress), and late-drought (90 days after applying water stress). Under maximum water holding regime, G. mosseae was more infective than G. deserticola and G. intraradices, but differences were not significantly different (P < 0.05). Predawn water potential was analogous for both mycorrhizal and control treatments whilst midday water potential was lower for control than for AMF treatments. Under mild and late drought, G. deserticola and G. intraradices were more infective than G. mosseae. Plants inoculated with G. intraradices had the highest predawn water potential and MWP. Mid-morning and midday stomatal conductance were similar and higher in seedlings inoculated with G. deserticola and G. intraradices. Under severe and late drought, infectivity was comparable and higher for both G. deserticola and G. intraradices. However, plants inoculated with G. intraradices displayed the highest growth, midday water potential, stomatal conductance and relative water content. Seedlings inoculated with G. mosseae and the controls had lost their leaves at -4 MPa water potential. Difference between Glomus species in the host response to water stress seemed to be related to the severity and duration of the stress. On the whole, inoculation of A. tortilis ssp. raddiana with G. intraradices resulted in increased plant growth and improved water status under severe and long-lasting drought, relative to G. deserticola and G. mosseae