Risposte fisiologiche e biochimiche di pioppi cresciuti in suoli arricchiti di ossido di calcio ed esposti a stress idrico.

Responses of plants to biotic and abiotic stresses had been widely investigated. However, fewer studies have been conducted on combined stress responses. The aim of this thesis is to study how the variation of plant nutritional status can influence the plant’s responses to drought stress. The research was conducted on poplar plants (Populus nigra), a species known to be particularly resistant to different stresses. The first phase of the work focused on the study of plant responses to nutritional stress. The stress was imposed by the addition of calcium oxide (CaO) to the soil, thus determining an alkaline pH. This soil condition reduces the bioavailability of certain nutrients, in particular iron (Fe) and phosphorus (P). During this phase, morphometric, physiological (chlorophyll content and stomatic conductance) and chemical (inorganic ions concentration) parameters were evaluated. The differences, between the two groups of plants (treated and not treated with CaO), were found only in the content of nutrients, confirming the effectiveness of the treatment. In the second phase of the experiment, the study extended to plant responses to combined stress, exposing poplars to a drought stress followed by a recovery (re-watering). The study was conducted through morphometric, physiological and biochemical analysis, extended to the measurements of the loss of hydraulic conductivity (PLC) of the stems and the content of soluble sugars, electrical conductivity (EC) and osmolarity in the xylem sap. The results show different responses of the two groups of plants (treated and not with CaO) when exposed to drought stress; in particular, treated plants have a better ability to recover both the hydraulic conductivity and the stomatic conductance than untreated plants. The combined stress also altered the levels of electrical conductivity, osmolarity and ionic content of the sap of poplars grown in alkaline soil, suggesting a possible role of some mineral nutrients in the recovery mechanisms. In conclusion, this work suggests that the treatment with CaO can have a priming effect on the responses of poplars to drought stress improving their recovery capabilities.