Nitrogen (N) is an essential nutrient for plant growth and development and is especially important in the production of high quality leafy green vegetables. In this experiment, leaf N concentration, chlorophyll concentration (Chl) and weight above fresh matter (AFM) of romaine lettuce (Lactuca sativa L. var. longifolia) were estimated by correlations between in situ SPAD and atLEAF readings. Lettuce was grown in high tunnels during 42 days and was irrigated at five nitrogen levels: 0, 4, 8, 12 and 16 mEq·L-1 of NO3-, based on the Steiner nutrient solution. The N concentration, Chl concentration and AFM were determined in the laboratory, while SPAD and atLEAF readings were measured in situ weekly. SPAD readings had high, positive and significant linear correlations with N (R2 = 0.90), Chl (R2 = 0.97) and AFM (R2 = 0.98); atLEAF readings had a similar linear correlation with N (R2 = 0.91), Chl (R2 = 0.92) and AFM (R2 = 0.97). Besides, SPAD and atLEAF readings had high, positive, and significant linear correlation (R2 = 0.96). Thus, SPAD and atLEAF meters can be used to non-destructively and accurately estimate the N status of lettuce, in a reliable and quick manner during the crop production cycle. In addition, atLEAF is currently more affordable than SPAD. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

Fruits is a scientific journal for original articles and reviews on fruit crops in temperate, Mediterranean, subtropical and tropical regions

Salinity is a major threat to the productivity of agroecosystems as it affects the soil structure and the osmotic potential of the soil solution, resulting in nutritional imbalances, Na toxicity and reduction in crop growth and yield. As Silicon (Si) has been considered a beneficial element for alleviating plant stress, the present study was performed to determine if it could enhance tomato plant tolerance to NaCl-salinity in a closed-loop hydroponic system. Plants were irrigated with solutions containing 0, 20 or 60 mM NaCl combined with 0 or 1.50 mM Si. Shoot dry weight and fruit yield decreased with salinity, however, Si partially restored biomass and yield when the solutions contained 20 mM NaCl. Shoot and root K decreased with salinity, however, supplementary Si restored K in plants with 60 mM NaCl. Root and shoot Si was unaffected by NaCl or Si, however, shoot Na increased. Nonetheless, compared to non-Si plants, Si-treated plants showed a 19% and 32% lower shoot Na concnetration in 20 and 60 mM NaCl-plants, respectively. Silicon partly alleviated the K/Na imbalance caused by salinity. Increased shoot K/Na and Ca/Na balances were correlated with higher shoot biomass. Supplemental Si allowed an 80% increase in peroxidase activity and proline in plants with 60 mM NaCl. Fruit yield under moderate salinity was partially restored by Si, due to an increased root Na exclusion, lower shoot Na, and improved K, Ca and K/Na balance, which was correlated with increased shoot growth, POD activity and proline concentration.