Basis for the fine tuning of deficit irrigation regimes in olive trees based on a novel water stress indicator from sap flow related measurements

Comunicación presentada en el ISHS Symposium 2016 "Sensing Plant Water Status“ Methods and Applications in Horticultural Science" Book of Abstracts 05– 07. October 2016 (Potsdam) GermanyThe expected climate conditions in the Mediterranean area demand an increasing use of sustainable water practices in agriculture, such as deficit irrigation (DI). The correct use of the most successful DI strategies, such as regulated deficit irrigation (RDI) requires both a good understanding of main physiological mechanisms involved in the response of plants to water stress, and the use of reliable and sensitive indicators of water stress. Stomatal conductance (gs) is a good plant-based indicator for irrigation purposes. Besides gs quick response to increasing water stress, stomatal closure limits photosynthesis and thus, it has important Implications for plant function, growth and yield. However, difficulties on monitoring gs curtails its use for irrigation scheduling purposes. Recently, our research group demonstrated that there is a robust correlation between the changes in sap flux density measured in the outer sapwood section of mature olive trunks and gs dynamics in the tree canopy, both in response to soil and air water deficit. Stomatal conductance of both sunny and shaded leaves can be reliably estimated from radial sap flux density. A biochemical model of photosynthesis was coupled to the estimated gs to determine the net CO2 assimilation rates (AN) along the season. As expected, our results show that plant growth (leaf area evolution was used as proxy) and yield were highly related to AN, and our approach was confirmed to be very sensitive to air and soil water deficits. However, our results show that the main determinant of yield was leaf area and not AN, although both are correlated and markedly affected by RDI. The use of our water stress indicator based on sap flux density appears to be a sensitive tool to schedule a RDI strategy in fruit tree orchards intended to control both vegetative growth and yield by imposing a certain degree of water stress to the trees.Peer Reviewe