Salzano, Melania (2020) Caratterizzazione di sostanze umiche ed estratti etanolici da compost verdi.Valutazione degli effetti antiossidanti e biostimolanti in piante di lattuga. [Tesi di dottorato]

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Humic substances play a fundamental role in improving the physical, chemical and biological soil properties, and determining carbon sequestration in soil and stimulating plant growth. Therefore, they are increasingly used for both soil and plant treatments. In this work, humic and hydroethanolic (water:ethanol; 30:70, v:v) substances have been isolated from composted green soil improvers, aiming to identify new products capable to deliver benefits to plant and soil, and enhance the reuse of vegetable wastes resulting from the production process of artichoke, coffee, pepper and lemon (pastazzo). The compost and their extracts have been subjected to molecular characterisation through analytical techniques such as DRIFT spectroscopy, GC/MS pyrolysis, and solid-state 13C-CPMAS-NMR spectroscopy.These analyses have revealed pronounced differences between the composition of compost and their extracts, mostly attributable to the different vegetable materials used for the composting stage. In particular, the humic substances extracted from artichoke compost have shown the highest values of hydrophobicity and aromaticity. The studied products have been tested in order to evaluate their biological activity and identify any possible structure-activity relation. ABTS and Folin-Ciocalteu tests have revealed a positive correlation between the antioxidant activity and the total content of phenols, with higher significant values, for both parameters, found for the humic substances from artichoke compost and lemon pastazzo. The effect exerted by humic substances on roots elongation has been proved through the germination test which was conducted on Zea mays. This effect resulted particularly pronounced in the case of humic substances from artichoke compost and was attributed to the relatively high content of phenolic compounds. Based on these results, humic substances from artichoke compost, in association with potassium humate extracted from lignite, have been tested, by soil application, on lettuce plants, distributing them both individually and combined in different percentages. Phenological results (dry biomass and chlorophyll content) have indicated a particularly positive effect only when the materials have been used individually. The secondary metabolome analysis, conducted through mass spectrometry IT-TOF, has revealed that humic substances from artichoke determine a mild stress condition, inducing a modulation in the content of several flavonoids. Phytotoxicity tests have been conducted on Lepidium sativum seeds using hydroethanolic extracts from coffee, artichoke and lemon pastazzo. The results not only have permitted to exclude the phytotoxicity of these materials, but have also revealed an effect on roots elongation. Such a result was particularly evident for artichoke and lemon pastazzo compost extracts applications. These products have been also tested by foliar application. Although any significant result has been appreciated, in terms of dry biomass and chlorophyll content, it is noteworthy the detection of small variations in the primary metabolome, as revealed by liquid-state 1H-NMR spectroscopy. In fact, it was detected a treatment-depending variation for some carbohydrates, organic acids and amino acids. Concluding, our results demonstrate that the substances considered for this thesis are capable to determine a biological effect on plants, whose action and intensity varies depending on the molecular composition of the products for the treatment. In addition, the fact that some of the studied products promote plant growth permits to consider the materials deriving from the recycle of waste plant biomass as ecologically sustainable sources of biostimulants for agricultural crops.

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