THE EFFECT OF SALINITY ON LEAF WATER RELATIONS AND CHEMICAL COMPOSITION IN THE SUB‐ANTARCTIC TUSSOCK GRASS POA COOKII HOOK F.

Abstract

SummaryIsolated tillers of the sub‐Antartic Maritime tussock grass Poa cookii responded to high concentrations of NaCl (0.3 to 0.7 M) in the root medium by markedly accumulating Na in the older leaves. Concomitant with this was a decline in leaf water potential (φ), osmotic potential (φ) and fresh weight: dry weight ratio. Inorganic solutes accounted for a greater proportion of the measured φ in older than in younger leaves and Na was the most important cation contributing to measured values of φ and φ Changes in the K, Ca and Mg concentrations in leaves exposed to NaCl in the root medium were related to changes in leaf water content rather than to remobilization of these elements within the plant. The results are interpreted as demonstrating a mechanism preventing injuriously high levels of Na in young, metabolically active tissue, rather than an osmoregulatory phenomenon. This suggests that P. cookii cannot be considered to be a true halphyte despite its frequent occurrence in the salt spray zone of many sub‐Antarctic islands.