Responses of spinach to salinity and nutrient deficiency in growth, physiology and nutritional value

Authors: Xu, Chenping; Mou, Beiquan

Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2015
Publication Date: 1/28/2016
Citation: Xu, C., Mou, B. 2016. Responses of spinach to salinity and nutrient deficiency in growth, physiology and nutritional value. Journal of the American Society for Horticultural Science. 141:12-21.

Interpretive Summary: High salinity conditions in agricultural soil and irrigation water is one of the most serious challenges faced by agricultural crops in the world. Another important limiting factor for crop production is soil nutrient deficiency. The effects of salinity and nutrient deficiency on spinach growth and nutrient content were evaluated in sand cultures under greenhouse conditions. Plants were watered every day with a standard plant nutrient solution, or a nutrient solution deficient in nitrogen, phosphorus or potassium in combination with a normal, or an elevated salt level. Salinity significantly decreased plant growth and leaf water content, and increased chlorophyll content. Nitrogen deficiency greatly reduced plant growth and chlorophyll content, but increased nutritional value regardless of salt treatment. Phosphorus and potassium deficiencies, similarly, decreased plant growth irrespective of salinity treatment, but increased chlorophyll content under no-salt conditions. Salt stress improved nutritional value by increasing carotenoid and flavonoid contents in full-strength nutrient solution. Nitrogen, phosphorus and potassium deficiencies affected different nutritional components positively or negatively depending upon the salinity level. For example, nitrogen deficiency increased anthocyanin and total phenolic contents, decreased carotenoids and flavonoids regardless of salinity treatment, and increased antioxidant capacity under no-salt conditions. These results suggest that reduced fertilizer application or mild salt stress might be utilized to improve the nutritional value of spinach with moderate or little yield reduction.

Technical Abstract: Salinity and nutrient depleted soil are major constraints to crop production, especially for vegetable crops. The effects of salinity and nutrient deficiency on spinach were evaluated in sand cultures under greenhouse conditions. Plants were watered every day with Hoagland nutrition solution, deprived of nitrogen (N), phosphorous (P) or potassium (K) for nutrient deficiency, either with or without 20/10 mM NaCl/CaCl2 for salinity treatment. Salinity significantly decreased shoot fresh and dry weight (FW and DW), leaf relative water content (RWC) and specific leaf area (SLA) relative to controls after four weeks of treatment, and increased chlorophyll content, maximum photochemical efficiency (Fv/Fm) and photochemical yield (Y(II)). N deficiency greatly reduced shoot FW and DW, SLA, and chlorophyll content, regardless of salt treatment. Y(II) and Fv/Fm were reduced by N deficiency and salinity treatment. P and K deficiency, similarly, decreased shoot FW and DW irrespective of salinity treatment, and increased chlorophyll content without salt stress. P deficiency increased Y(II) and Fv/Fm under both control and salt treatment. Salinity and nutrient deficiency also affected the nutritional value of spinach. Salt stress increased carotenoid and flavonoid contents, and reducing power in full-strength Hoagland solution, and decreased leaf ferrous ion chelating ability (FICA). Nutrient deficiency increased reducing power regardless of salinity treatment. N deficiency increased anthocyanin and total phenolic contents, decreased carotenoids and flavonoids regardless of salinity treatment, and increased antioxidant capacity under no-salt conditions. P deficiency increased carotenoid and flavonoid contents under no-salt condition, and enhanced total phenolic content and reduced FICA and amino acid content under salt stress. K deficiency increased total phenolics, carotenoids and flavonoid contents, and antioxidant capacity under non-salt condition, but decreased FICA regardless of salinity treatment. These results suggest that spinach nutritional value could be improved with only moderately or slightly reduced yield through cultural practices that impose either low fertilizer levels or mild salt stress.