Uptake of Mn and Zn by Cucumber Grown in Closed Hydroponic Systems as Influenced by the Mn and Zn Concentrations in the Supplied Nutrient Solution

Abstract

The objective of the present experiment was to estimate the uptake of manganese (Mn) and zinc (Zn) by cucumber in closed hydroponic systems at different Mn and Zn concentrations in the recycled nutrient solution under Mediterranean climatic conditions. The obtained data might be used to manage Mn and Zn supply in closed hydroponic crops of cucumber grown in Mediterranean greenhouses and avoid their accumulation to toxic levels. Four Mn levels (10, 40, 80, 120 μM) at a standard Zn concentration (6 μM) and four Zn levels (6, 20, 40, 60 μM) at a standard Mn concentration (10 μM) in the solution supplied to compensate for nutrient and water uptake by plants were applied as experimental treatments. The actual uptake concentrations of Mn and Zn were estimated by applying two different methods. The first method was based on the removal of Mn, Zn, and water from the recycling nutrient solution, whereas the second method was based on the total quantities of Mn and Zn that were recovered in plant biomass in combination with the total water uptake. Both methods gave similar uptake concentrations for Mn in the low-Mn supply level and Zn in all Zn levels. However, in the three higher Mn supply levels, the values estimated on the basis of nutrient removal from the recirculating nutrient solution were significantly higher than those found by measuring the total Mn content in plant biomass. These discrepancies in the three high-Mn treatments were possibly caused by partial immobilization of Mn by oxidizing bacteria in the nutrient solution. The objective of the present experiment was to estimate the uptake of manganese (Mn) and zinc (Zn) by cucumber in closed hydroponic systems at different Mn and Zn concentrations in the recycled nutrient solution under Mediterranean climatic conditions. The obtained data might be used to manage Mn and Zn supply in closed hydroponic crops of cucumber grown in Mediterranean greenhouses and avoid their accumulation to toxic levels. Four Mn levels (10, 40, 80, 120 μM) at a standard Zn concentration (6 μM) and four Zn levels (6, 20, 40, 60 μM) at a standard Mn concentration (10 μM) in the solution supplied to compensate for nutrient and water uptake by plants were applied as experimental treatments. The actual uptake concentrations of Mn and Zn were estimated by applying two different methods. The first method was based on the removal of Mn, Zn, and water from the recycling nutrient solution, whereas the second method was based on the total quantities of Mn and Zn that were recovered in plant biomass in combination with the total water uptake. Both methods gave similar uptake concentrations for Mn in the low-Mn supply level and Zn in all Zn levels. However, in the three higher Mn supply levels, the values estimated on the basis of nutrient removal from the recirculating nutrient solution were significantly higher than those found by measuring the total Mn content in plant biomass. These discrepancies in the three high-Mn treatments were possibly caused by partial immobilization of Mn by oxidizing bacteria in the nutrient solution.