Investigation of nutrient solutions for the hydroponic growth of plants
Hydroponics is used extensively in food production and plant research, allowing optimal control over the supply of elements to the plant. In hydroponics, nutrient can be delivered via a solution that is supplied to the growing plant or as a seed coat or treatment that is applied to the seed before sowing and germination. The form in which the nutrients are supplied to the plant influences their bioavailability, up-take, and distribution within the plant. Commercially produced hydroponic nutrients are typically supplied as two separate concentrated solutions. If these are mixed before being diluted then precipitates are formed which limit the bioavailability of certain elements in the nutrient solution. The chemical nature of the precipitate has been investigated by XRD, XRF, ion-chromatography and IR and Raman spectroscopies, with the aim of understanding its composition. Mass spectrometry is a highly sensitive analytical technique which has been applied to the monitoring of uptake and distribution of elements and compounds in plant tissue. Techniques including MALDI-MS, LA-ICP-MS and HPLC-ICP-MS have been utilized in the work presented here to demonstrate the distribution and accumulation of elements and compounds within plant material that has been grown hydroponically. The use of a zinc based seed coating as a nutrient source for barley seeds in a hydroponic fodder production system has been investigated. The effect of the zinc on the yield and dry mass of the fodder was determined. The total zinc content in the fodder has been determined using ICP mass spectrometry. A method to map the location and distribution of zinc and other metallic elements in seeds and the fodder plants using Laser-Ablation ICP Mass Spectrometry LA-ICP-MS has been developed. Selenium is an essential element for human health. Broccoli is known to be a hyper-accumulator of selenium and the use of selenium-containing hydroponic nutrients for the biofortification of broccoli with selenium is presented. Laser-Ablation ICP Mass Spectrometry LA-ICP-MS has been used to monitor the accumulation and distribution of selenium in the broccoli plants. Imaging MALDI-MS has allowed the demonstration of the nitrogen cycle in plants and to show pictorially that atoms and molecules from dead plants are incorporated into new life. Radish plants were grown hydroponically using a nutrient solution system containing isotopically-enriched nitrogen-15 KNO3 (98% labelled) as the only source of nitrogen. Plants were cropped and left to ferment in water for 2 weeks to create a radish "tea", which was used as a source of nitrogen for radish grown in a second hydroponics experiment. After 5 weeks of growth, the radish plants were harvested and cryosectioned, and sections were imaged by positive-ion MALDI imaging. The presence of labelled species in the plants grown using 15N KNO3 as nutrient and those grown from the radish "tea" was readily discernible. The uptake of 15N into several identifiable metabolites has been studied by MALDI-MS imaging.
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