ARI Biennial Review for 2018-2019

The effects of phosphorus supply limitation on photosynthesis, biomass production, nutritional quality, and mineral nutrition in lettuce grown in a recirculating nutrient solution In this study, we investigated the impact of phosphorus (P) supply levels (0.8, 1.3 and 1.8 mM) in two green leaf lettuce ( Lactuca sativa L.) types, namely ‘Romaine’ (cv. Nader), and ‘Lollo’ (cv. Bionda) grown in a recirculating nutrient solution. The biomass yield of the ‘Romaine’ type was reduced by 15% at the lowest P supply (0.8 mM), and plants showed reduced photosynthetic function (i.e. net photosynthesis, stomatal conductance, quantum yield and electron flow) and increased root/shoot ratio. On the other hand, the ‘Lollo’ type maintained photosynthetic rates and biomass accumulation in all cases and proved less sensitive to low P levels in the NS. In addition, lowering P supply boosted P-use efficiency (kg biomass kg -1 P supply) in both types of lettuce. Nutrient to water uptake ratios of macro nutrients N, P, K, Ca and Mg were determined as follows: (i) 16.0, 1.3, 9.1, 3.1 and 0.9 mmol L -1 , respectively for ‘Romaine’, and (ii) 16.4, 1.3, 9.1, 3.3 and 0.9 mmol L -1 , respectively for ‘Lollo’. The current experimental results suggest that, reducing the P supply to lower levels than those currently recommended for lettuce crops grown in closed hydroponics, considerably improves the P use efficiency in Mediterranean greenhouses without compromising yield. (D. Neocleous) Seasonal variations of antioxidants and other agronomic features in soilless production of sweet peppers and fresh aromatic herbs Our results indicate that in Mediterranean greenhouses during late autumn and winter light conditions (solar and ultraviolet radiation) can be insufficient to stimulate brightly coloured peppers with elevated content of antioxidants (e.g. phenolics, ascorbic acid and carotenoids). This suggests that a proper selection of greenhouse type and cover material in response to plant-light interception in conjugation with the selected crop and cultivation system may be a prerequisite to optimise environmental conditions for plant growth and elevated antioxidant phytochemicals in yearly-grown sweet coloured peppers in Mediterranean greenhouses. ( D. Neocleous). Furthermore, selected aromatic herbs of the Lamiaceae family, namely basil ( Ocimum basilicum ), mint ( Mentha viridis ), balm ( Melissa officinalis ) and thyme ( Thymus vulgaris ), were grown in Cyprus greenhouses under soilless conditions. Soilless greenhouse production of fresh aromatic herbs under Mediterranean climatic 49 NATURAL RESOURCES AND ENVIRONMENT