Stomatal and hydraulic water transport factors in mycorrhizated olive trees

Water uptake and transport are complex processes affected by root hydraulic conductance and water utilization, as mediated by leaf. Arbuscular mycorrhizal (AM) fungi may colonize roots and regulate stomatal behaviour contributing to the overall water economy of the tree.This study test whether AM colonisation has a beneficial effect on total root hydraulic conductance and leaf gas exchange parameters in olive trees both well irrigated and under drought.Approx. 20 2-year old potted olive trees were inoculated with Glomus intraradices, 10 inoculated trees were kept well irrigated (WI) while the remaining were allowed to dry up (D) till a value of -2 MPa predawn leaf water potential (Y). Additional 20 trees were not inoculated and served as control.Hydraulic conductance (K, kg s-1 MPa-1) was determined by a HCFM (Dynamax, Inc. USA) (0.1- 0.5 MPa of applied pressure). Leaf transpiration (E), assimilation (A) and stomatal conductance (gs) was appraised through the LI-6400 (Li-Cor Inc., NE, USA).Drought in non-inoculated trees induced a decline of midday K from 1.1±0.1 (SE) to 0.9±0.1 kg s-1 MPa-1, AM fungi maintained K stable or even higher at 1.3±0.1 kg s-1 MPa-1 (inoculated D trees). A positive impact on hydraulic transport (~23% increase of K) was also detected in mycorrhizated WI trees.In WI trees, average daily A remained similar in control and mycorrhizated trees (~ 4 mmol CO2 m-2 s-1), concomitantly it was registered a significant reduction of E and gs in mycorrhizated WI trees compare to non mycorrhizated WI. In D trees, a similar response of E and A was detected, while gs was not clearly affected by AM.This study revealed that AM may regulate both K and some gas exchange parameters in both WI and D olive trees and that the fungi improved the water use efficiency at leaf scale. It could be concluded that knowledge and improvement of soil biodiversity level (including AM) through sustainable practices may be in favour of an optimal water use in agriculture.