Effects of drought/recovery cycles on tissue osmoregulation, water relations and root exudation in plants

Not all organic compounds synthesized by plants undergo conversion into structural carbohydrates; conversely, a substantial portion of photosynthesized sugars is designated for the formation of non-structural carbohydrates (NSCs). Among the most significant and enigmatic NSCs are root exudates, comprising predominantly polysaccharides, amino acids, organic acids, and phenolic compounds. The carbon emissions from roots are considerable, amounting to approximately 11% of the carbon fixed by leaves during photosynthesis and constituting 27% of the carbon allocated to the roots. To elucidate the mechanisms triggering the release of root exudates in plants and their impact on the growth of soil microorganisms, particularly truffles, two monitoring stations were established in diverse locations. These stations collected plant physiology data using sensors such as dendrometers, sap flow sensors, and environmental sensors. Analysis of environmental data revealed that truffle growth was not influenced by conventional parameters like humidity and temperature. Instead, it proved imperative to consider the physiology of the plant with which the fungus forms a symbiotic relationship and from which it derives nourishment. Examination of dendrometer and sap flow data disclosed distinctions between truffle-producing and non-productive plants. Productive plants demonstrated superior dehydration control, attributed to osmoregulation mechanisms involving the accumulation of osmolites. The study also entailed experiments with maize and Quercus ilex L. plants to explore osmoregulation activities and the release of root exudates. Results suggested that osmolites, including sugars, could be released from roots after stress and recovery phases, as evidenced by changes in osmolality in leaf and root tissues during such cycles. This research challenges prevailing beliefs regarding truffle growth conditions, presenting a fresh perspective that integrates the symbiotic nature of mycorrhizal fungi. The findings significantly contribute to a more comprehensive understanding of plant-water interactions and osmoregulation mechanisms, offering valuable insights into the release of root exudates and their potential effects on forest ecosystems.