The very first results obtained during the Outgoing Phase were: 1) the optical technique was used for the first time to monitor simultaneously xylem embolisms formation in roots, stems, and leaves in entire, intact olive seedlings; (2) roots were identified as the most resistant organs to these embolisms formation, in contrast with previous studies that pointed at the roots as more vulnerable tissues than core tissues (stems); and (3) a relatively high variation in resistance was found between individuals, between tissues, and within tissues. As this work did not assess the impact of plant hydraulics on stomatal functioning, a specific experiment was conducted also in olive aiming at determining whether the hydraulic pathway from the soil to the leaf is dynamic or static during stomatal closure. Results included: (1) the development of a new hydraulic method to partition the hydraulic pathways from the soil to the leaves, and (2) an observed decrease in the root water transport capacity under moderate drought conditions that worked as a hydraulic signal to limit stomatal opening, helping the plant to conserve water and isolating it from the drying soil.
Directly related to AgroPHYS, we expanded our knowledge on how hydraulic traits can be decisive for protecting plants against drought negative effects by working with different olive genotypes. Moreover, the application perspective of AgroPHYS was also addressed by developing robust, physiologically based tools for irrigation management, demonstrating that combining the three main fields of research of AgroPHYS is not only possible but fundamental for progressing on optimizing water use in agriculture.
In addition to these direct outcomes from AgroPHYS, and thanks to the participation in Synchrotron-based campaigns, we demonstrated that the optical technique was equally effective as hydraulic and micro-tomography techniques for measuring hydraulic resistance thresholds of water stress.
During the entire Incoming Phase, experiments were mainly focused on applying the new plant physiological knowledge acquired during the Outgoing Phase on the experimental orchard ‘La Hampa’ from the IRNAS-CSIC. Six fruit tree species were physiologically, extensively characterized, and monitored with meteorological, soil, and plant sensors.
As an overview of the overall results of AgroPHYS we can say that (1) knowing the resistance to water stress of agricultural species is pivotal under a global change context; (2) however, these levels of water stress should not be reached in fruit tree orchards and, in fact, plants avoid that by closing stomata; (3) limitations on productivity derived from this stomatal closure appear to be related with the belowground capacity to water uptake; and (4) we thus demonstrated that stomatal conductance should be our target to monitor water stress in fruit orchards.
Exploitation and dissemination of these results have been addressed by presenting them in several Xylem International Meetings, in seminars in both University of Tasmania and Researcher Centres in Spain, starting a collaboration with soil scientist at the University of Bayreuth (Germany), and publishing several papers in highly ranked journals, giving extra support to our conclusions.
