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The adaptation capacity of olive trees to different environments is well recognized. However, the presence of microorganisms in the soil is also a key factor in the response of these trees to drought. The objective of the present study was to elucidate the effects of different arbuscular mycorrhizal (AM) fungi coming from diverse soils on olive plant growth and water relations. Olive plants were inoculated with native AM fungal populations from two contrasting environments, that is, semi-arid - Freila (FL) and humid - Grazalema (GZ) regions, and subjected to drought stress. Results showed that plants grew better on GZ soil inoculated with GZ fungi, indicating a preference of AM fungi for their corresponding soil. Furthermore, under these conditions, the highest AM fungal diversity was found. However, the highest root hydraulic conductivity (Lp(r)) value was achieved by plants inoculated with GZ fungi and growing in FL soil under drought conditions. So, this AM inoculum also functioned in soils from different origins. Nine novel aquaporin genes were also cloned from olive roots. Diverse correlation and association values were found among different aquaporin expressions and abundances and Lp(r), indicating how the interaction of different aquaporins may render diverse Lp(r) values.

Olive trees are exposed to drought and arbuscular mycorrhizal (AM) symbiosis may enhance their drought tolerance. Here, AM inocula from different origin (humid or arid) were used in order to determine how AM fungi or soil origin modify the response of olive trees to drought. Furthermore, nine novel aquaporins from olive trees were cloned. It was found that the AM from the humid origin were the most effective in enhancing drought tolerance, even in the arid soil.