Trace elements in the soil-plant system

Contact: Beatrice Pezzarossa (Unit of Pisa)
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If present in optimal concentration ranges, some trace elements (Zn, Cu, Mn) are important essential elements for the nutrition of higher plants and for animal nutrition. Others (Hg, Pb, Cd) are potentially toxic. Plants that are able to accumulate microelements in their tissues can be used both to supplement a deficient mammalian diet and to remove trace elements from contaminated soil. The soil-plant system is instrumental in human nutrition and forms the basis of the ‘food chain’ in which there is micronutrient cycling. Better nutrient cycling contributes towards a better ecological environment resulting in an ecologically sound and sustainable flow of trace elements. Soil-plant system strategies that have been adopted to improve human micronutrient nutrition mainly include: i) improvement in our knowledge of the trace elements flow from soils to the edible parts of crops, ii) a better knowledge of the relationship between the content and bioavailability of micronutrients in soils and those in edible crop products.


Research

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Our research is aimed at evaluating trace elements in the soil, their chemical availability and bioavailability, their uptake by cultivated plants, their translocation and accumulation in plant tissues. Part of our research focuses on the dynamics of selenium (Se) in the soil-plant system and the study of the physiological and metabolic effects induced by selenium accumulation in cultivated plants. At higher concentrations, Se can be toxic, and the margin between Se toxicity and essentiality is quite narrow. We used agricultural crops both to remediate selenium-contaminated soils and to increase the daily selenium intake of consumers after soil supplementation using inorganic or organic selenium sources. Brassica juncea and their associated microbes have been used for the environmental cleanup of selenium-contaminated soil. Brassica juncea directly participates in selenium decontamination through both phytoextraction and putative volatilisation. We investigated the effects of the addition of selenium on production and fruit ripening. In tomato we found that Se, due to its antioxidative role, is effective in reducing plant growth, delaying the onset of plant senescence and fruit ripening, prolonging shelf-life, and, at the same time, has positive effects on human health.

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In lettuce and chicory, selenium is effective in decreasing the production of ethylene and phenylalanine ammonia-lyase activity, consequently improving the quality of leafy vegetables and shelf life in both species. The addition of Se in a nutrient solution has been found to be a useful system for providing enriched leafy vegetables. The floating system can be used to modulate the availability of Se in nutrient solutions and to grow vegetables with the optimal Se content for human health.

In peach and pear foliar and fruit, selenium spraying appears to be effective in increasing the selenium content of fruit. The enhanced selenium concentration affected the shelf life of fruit by delaying the reduction in flesh firmness and fruit ripening, thus positively affecting fruit storage. Future research will focus on the mechanisms through which Se is effective in delaying fruit ripening, such as ethylene production and accumulation. Studies will also evaluate whether the addition of higher amounts of Se and the consequent higher accumulation of Se in fruit could positively affect fruits post harvest, thus prolonging shelf-life and leading to an increase in fruit consumption without any toxic effects on humans. The research group participated in the Organizing and Scientific Committee of the three editions of the National Scientific Congress ‘Soil Quality, Food and Health’ (Napoli, May 20-22, 2010; Bari, October 22-24, 2008; Palermo, October 24-26, 2007).