Hydrochar application for improving plants performance under stress: a promising pathway to support the transition to a circular economy

Climate change is exposing plants to an increasing number of events in which combined effects of heatwaves and drought co-occur. These anomalous climatic conditions have already caused, at global scale, consistent plant death in natural ecosystems and biodiversity loss. And further negative impacts on vegetation is expected in the next future, especially in Europe, as a consequence of forecasted warming. Based on the key role of plants on water cycle as well as on carbon cycle, tree mortality has important cascade effects on ecosystems and related services and, not last, it may further accelerate climate change too. It is very urgent to develop action(s) aimed at limiting climate-change-driven loss of plant productivity. Moreover, it is very relevant to acquire detailed knowledge on the combined effect of heat and drought stress on plant health, i.e., the main environmental constraints leading to climate-change driven plant dieback. In fact, our understanding of plants' response to warmer and drier conditions is scarce. In the frame of reducing food waste and using it for creating further value material (circular economy policy), in the last years great attention has been paid on hydrothermal carbonization (HTC) technology that allows to convert bio waste into high quality hydrochar (HC). HC is a carbon based solid fraction and can be used as an energy source, a feedstock to produce bioproducts and even as a soil amendment. Regarding the use as a soil amendment, some studies suggest that enriching the soil with hydrochar in place of compost can have positive effects on plant health, including an increase in resistance to biotic and abiotic stress. However, to the best of our knowledge, the actual effects on HC use in plants, in the frame of the key plants’ role on soil-plant water relations, have never been investigated. By contrast, it is very urgent to have detailed knowledge on the actual benefits of using hydrochar as soil amendment in order to head the research efforts towards cost-effective solutions. The present project mainly aims to elucidate the role of hydrochar addition, obtained by bio waste, in mitigating the most common climate-change-driven environmental constraints (i.e., drought and heat) in two ecologically and economically relevant species: Populus nigra L. and Helianthus annuus L. Particular attention will be paid to plant-water relations and cell dehydration damages due to the recently emerging role of critical water content values in leading to drought-driven plant mortality. The transcriptomic investigation of these samples will offer a more detailed knowledge on molecular mechanisms involved in the plants’ responses to different stresses with or without HC. Further, the project will advance current knowledge on the effects of drought and heat on the productivity and ecophysiology of the study species.