Growth responses of Mesembryanthemum crystallinum to different nitrogen concentrations and selected growing media for hydroponics systems

Abstract

Mesembryanthemum crystallinum L. is a perennial halophyte that originated in southern and eastern Africa and is now widespread throughout the world. Recent studies have shown that the plant can grow in salty soils without losing its nutritional value. However, little has been reported about factors that modulate quantity of secondary metabolites in the plant. In this study, the twin effect of different concentrations of nitrogen (0, 0.36, 0.6, 0.8 g/L) and growing media (LECA clay, peat, vermiculite and silica sand) on the production of plant growth, mineral content, proximate and antioxidant metabolites in hydroponically cultivated M. crystallinum was investigated. The untreated plants (0 g/L of N) were used as the control. Findings from this study suggest that a combination of properly formulated nutrient solution and growing media can significantly improve plant development in M. crystallinum. Vermiculite-infused nutrient solutions of 0.8 g/L and 0.6 g/L of N fertilizer showed a considerable improvement in plant growth metrics when fed to M. crystallinum. It can therefore be concluded from this study that M. crystallinum can be grown hydroponically. As previous studies stated that M. crystallinum can only grow in coastal areas. In this study, the chlorophyll content of M. crystallinum treated with different nitrogen concentrations and grown in hydroponics with various growing media was examined. An instrument provided by Konica-Minolta called the Soil Plant Analysis Development (SPAD-502) meter was used to measure the chlorophyll concentration at the beginning of growing season (week 2) and just before harvesting (week 12). The LECA clay supplemented with 0.6 g/L of nitrogen concentration produced the highest chlorophyll during week two of the experiment which is statistically equivalent to values obtained in plants grown with vermiculite (0.6 g/L), peat (0.8 g/L), LECA clay (0.8 g/L) and peat (0.6 g/L). The total phenols, flavonol, flavanol of the crude extract was determined while the antioxidant content was determined using the DPPH, FRAP and ABTS antioxidant assays. It was observed that leaves of M. crystallinum grown in LECA clay supplemented with N fertilizer (0.36 g/L) had the highest total phenolic content (6.4 mg GAE/g) than leaves from other treatments. The highest mean value (2.9 mg QE/g) of flavonols was found in LECA clay supplemented with 0.36 g/L of N fertilizer, followed by N fertilizer treated peat (2.7mg QE/g). Nutrients and proximate were done using AOAC while minerals were determined using inductively coupled plasma-optical emission spectrometer (AOAC).The highest ADF content was obtained from LECA clay supplemented with 0.8 g/L nitrogen concentration, highest ash content from vermiculite with no nitrogen concentration, highest fat content was obtained from silica sand with no supplementation, the highest moisture content was obtained from silica sand with 0.8 g/L nitrogen supplementation, whereas the highest NDF was contained from LECA clay with 0.36 g/L concentration. The findings of this study revealed that although, nutrients and proximate composition of M. crystallinum is intensely influenced by different growing media and various nitrogen concentration. Also, this study showed that the increased of nitrogen in the growing media cannot be useful in production of proximate composition of M. crystallinum. This study suggests that M. crystallinum can be grown in any type of growing media and can be irrigated with municipal water and require nitrogen fertilizer for optimum growth.