by Andrea Visca, Gaetano Perrotta, Luciana Baldoni, Ornella Calderini, and Annamaria Bevivino
La drought represents a growing threat to the olive cultivation in the Mediterranean regions, where water availability is increasingly limited due to climate change. Scenarios predict an increase in temperature and a change in precipitation patterns, resulting in increased evaporation, reduced available water in the soil, and increased soil salinity.
The ability of plants to cope with water stress conditions depends not only on their physiological characteristics, but also on complex interactions with microorganisms present in the soil and roots, real “invisible allies” which help plants to resist when water is scarce.
Within the project BIOMEnext funded by the PRIMA 2021 programme (partnership for research and innovation in the Mediterranean area), the researchers explored the soil microbiome e associated with the roots of traditional and native olive genotypes, for example the wild olive trees, i.e. cultivars that show a certain resilience to water stress, in order to develop new consortia of beneficial microorganisms capable of increasing plant tolerance to climate change, a major challenge for agriculture.
In particular, olive groves located in central Italy, near Perugia, were chosen in two experimental sites: Boneggio and Lugnano. The researchers analyzed the resilience and functional adaptation of microorganisms present in the roots and soil of four olive cultivars (Arbequina, Koroneiki, Chemlal de Kabilye and Shengeh, originating respectively from Spain, Greece, Algeria and Iran), comparing normal irrigation conditions with prolonged water stress, in different seasons of the year.
The first two cultivars (Arbequina and Koroneiki) have been reported in the literature as more sensitive to drought than the last two (Chemlal and Shengeh). The project, coordinated by the University of Perugia, involves ENEA and other partners from France, Lebanon, Morocco, Spain, and Tunisia. The study showed that, in soil, the microbiome remains relatively stable even in drought conditions, thanks to the functional redundancy of microbial communities; instead, the rhizospheric and endophytic microbiome changes: the plant selects the bacteria that are most useful for resisting the lack of water, thus improving its drought tolerance.
This process promotes better nutrient absorption and strengthens roots, improving the plant's ability to retain water. The researchers suggest that olive tree roots are able to actively select the most beneficial microorganisms through the root system, thanks to root exudates, thus enriching the microbiome with taxa capable of mitigating the effects of drought, performing key functions such as nitrogen fixation, chemotaxis, and phytohormone production. This selection allows plants to improve nutrient uptake under conditions of limited availability and strengthen root structures, increasing water retention.
Among the most relevant bacteria, the genera Solirubrobacter, Microvirga e Pseudonocardia emerge as true protagonists of the response to droughtThese microorganisms perform complementary functions, including nutrient recycling, nitrogen fixation, and modulation of plant hormones. Their presence suggests they could be used as the basis for synthetic microbial consortia designed to strengthen plant drought tolerance and improve the productivity of Mediterranean olive groves.
Through the formulation of synthetic communities (SynComs) that replicate the identified microbiome, These solutions could be applied directly in the field to support plant health and productivity under water stress conditions..
The results of the study offer new ecological knowledge ed a real operating manual for sustainable agriculture. From an applied perspective, the findings open up interesting perspectives for Mediterranean agriculture: from the integration of microbiome-based approaches, such as microbial consortia or targeted inoculants, to the selection of cultivars capable of attracting favorable microbial associations, in order to sustain productivity in conditions of water scarcity. Understanding the mechanisms by which microorganisms support plants opens the way to natural strategies to increase the resilience of olive trees, without resorting exclusively to chemical interventions or intensive irrigation. In this way, plant-microbiome interactions can become natural solutions to increase the productivity and sustainability of Mediterranean agroecosystems in an increasingly arid climate.
