Cellular osmotica of plants in relation to sediment nitrogen and salt content in mangroves and saltmarshes at Western Port, Victoria

Abstract

Sediments from mangrove and saltmarsh areas at Yaringa, Western Port contained high concentrations of chloride (c. 330-2100 mmol per litre of interstitial water) and sodium (c. 320-1900 mmol 1^-1). The concentrations recorded during the study were highest in March and lowest in July-August; salinity in the marsh during summer was considerably higher than that commonly reported for saltmarshes in other parts of the world. Sediment ammonium contents (c. 180-580 nmol per cm³ of fresh sediment) were variable across the marsh and throughout the sampling period, with there being little overall pattern to these changes. In contrast, concentrations of nitrate plus nitrite were low (< 100 nmol cm³) for most of the year except for a period in March when they were extremely high (c. 1100-1800 nmol cm^-3). The leaf-cell sap of all saltmarsh and mangrove plants contained high concentrations of chloride (c. 300-1200 mmol per litre of cell sap), sodium (c. 280-900 mmol l^-1) and potassium (c. 40-200 mmol l^-1). Glycinebetaine was accumulated in the leaf-cell sap to concentrations of up to about 90 mmol l^-1 by Atriplex paludosa, Avicennia marina, Sarcocornia quinqueflora, Sclerostegia arbuscula and Suaeda australis. Proline and glycinebetaine were accumulated by Limonium australe, Samolus repens, Selliera radicans and Triglochin striata, but no species accumulated proline alone. Concentrations of inorganic osmotica in the foliage were generally highest in March, whereas glycinebetaine and proline were at their most concentrated in April. No significant relationship was detected between concentrations of organic osmotica in the plants and that of salt or inorganic nitrogen in the sediments.