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Understanding how plants overcome drought by controlling stomatal function: applicability and impacts on agriculture

Periodic Reporting for period 1 - AgroPHYS (Understanding how plants overcome drought by controlling stomatal function: applicability and impacts on agriculture)

Reporting period: 2017-08-01 to 2019-07-31

We live currently under a global crisis where the increase of the world population and therefore, the food demand, is placing agriculture under a context of urgency, because it will need to produce this food without wasting the water necessary for that production. In addition to that, the climate crisis and the increase in water scarcity, considering that agricultural water use can be up to 80% of available fresh water, make essential the improvement of agricultural practices and the development of more efficient irrigation strategies. Drought events, more and more frequent and severe, cause plant water stress, a functional and structural plant response to low water availability, that reduces the productivity of a crop. Thus, an understanding of the impact, mechanisms and traits underlying drought tolerance in agricultural plant species is essential to increase the efficiency of irrigation strategies and to improve productivity. The impacts of this on society are direct, representing major European priorities: optimizing agriculture in a changing climate with reduced water availability and a growing population.
The AgroPHYS project aims to combine three important fields of research (diagram attached) to deal with this urgent need. On one hand, plant sensors can be used to monitor water stress in real time and use these outputs to improve irrigation strategies. On the other, process-based models, also called mechanistic or physiological models because they integrate detailed plant physiological processes and mechanisms, can be used to predict how global change is impacting plants. However, the signal outputs from plant sensors are still difficult to interpret and relate to water stress, and process-based models can be very complex with uncertainties in daily and seasonal evolution of the physiological parameters involved. So, currently, it is quite challenging to apply these approaches separately, and therefore we need a third field of research to help us to combine them and make them complementary for each other. That is, a fundamental understanding of the physiological mechanisms of a plant under water stress. With this knowledge we will be able to place the signal outputs of the plant sensor within a physiological context, which will help us to simplify process-based models without losing the link with physiological processes and thus to accommodate new experimental knowledge on these models, opening the doors to new hypotheses to be tested. During the reporting period from 01/08/2017 to 31/07/2019, Dr. Rodriguez-Dominguez mainly focused her research on exploring in depth the physiology of the plant and its response to drought.
When AgroPHYS project officially started (01/08/2017), Dr. Rodriguez-Dominguez was already at Prof. Brodribb's lab since November 2016 involved in a project highly related with one of the objectives of AgroPHYS ('Assessing the impact of hydraulic signals on stomatal behavior, focusing on leaf and root levels, during water stress and recovery'). This previous period as a Postdoctoral Research Fellow in Plant Ecophysiology at the outgoing institution allowed key training in fundamental techniques and skills needed for AgroPHYS (training in the optical technique for visualizing the formation of air bubbles within the xylem vessels, learning the software ImageJ through a Fiji/ImageJ Workshop, training in the preparation of cross-sections of different plant tissues, training in the preparation of samples and extraction of leaf abscisic acid) and greatly benefited AgroPHYS kick-off.
The very first results obtained during the reporting period, presented in the 3rd Xylem International Meeting in September 2017 and published in a high ranked journal (Rodriguez-Dominguez et al., 2018, New Phytologist), 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) a consistent pattern of root>stem>leaf in terms of resistance to embolisms formation was found, identifying roots as the most resistant organs, 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 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 in also in olive aiming at determining whether the hydraulic pathway from the soil to the leaf is dynamic or static during stomatal closure. This work has recently led to a publication in an international high ranked journal (Rodriguez-Dominguez & Brodribb, 2019, New Phytologist). Results from this work included (1) the development of a new hydraulic method to partition the hydraulic pathways within a plant, 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 produce stomatal closure, helping the plant to conserve water and isolating it from the drying soil. These results will be presented in the 4th Xylem International Meeting in September 2019. At the end of the Outgoing Phase, Dr. Rodriguez-Dominguez presented AgroPHYS’s results so far to a variety of students, PhD students and Professors in the seminar cycle of the School of Biological Sciences of UTAS. She took advantage of this seminar and acted as MSC Ambassador to motivate PhD students about the excellent working conditions and the great opportunities for boosting their research careers that the MSCAs offer.
Drought can cause important economic losses due to a decline in productivity. Therefore, new insights on how plants overcome drought resulted from AgroPHYS outcomes will have great impacts on reducing these economic losses by optimizing water use in agriculture and even improve the quality of the final product. For instance, in agriculture there is an irrigation strategy called Regulated Deficit Irrigation based on applying exactly the water that our crop needs at each of its phenological stage, because it is known that depending on which stage the crop is, it will be less or more resistant to drought. These strategies can be highly optimized by improving the physiological knowledge behind these different resistances at different phenological stages. Moreover, this knowledge will allow to place plant sensor outputs in a physiological context, so we will be able to monitor these physiological variables over time and to use them as inputs for improving predictions of climate change on plants through mechanistic models and for providing new hypotheses to be tested. However, this will be only possible if there is good communication between physiologist and agronomist to improve the irrigation strategies, between them and engineers and companies to minimize the costs of technologies in agriculture, and between them and mathematicians and modellers to translate physiological mechanisms into equations.
Diagram of the interaction of the three main approaches of AgroPHYS.