
%0 Journal Article
%A Allaway, WG 
%A Pitman, MG 
%A Storey, R 
%A Tyerman, S 
%A Ashford, AE 
%T Water Relations of Coral Cay Vegetation on the Great Barrier Reef: Water Potentials and Osmotic Content
%J Australian Journal of Botany
%D 1984/10/01
%V 32
%N 5
%P 449-464
%K 
%R https://doi.org/10.1071/BT9840449
%U https://www.publish.csiro.au/paper/BT9840449 
%X Foliage of 18 species from One Tree Island, a coral cay at the southern extremity of the Great Barrier Reef, contained abundant K+, Na+, Mg2+, Ca2+ and Cl-, although very high NaCl levels characteristic of halophytes were found only in Sesuvium portulacastrum. Four species contained large quantities of compatible solutes: glycinebetaine in Achyranthes aspera, proline in Sesuvium, Scaevola taccada and Melanthera biflora, and &#946; -dimethylpropiothetin in Melanthera. The ability to make such S-containing compatible solutes as the last mentioned may be especially important for maritime species. Most of the calcium and a large proportion of the magnesium were in insoluble form in Melanthera, Argusia argentea and Pisonia grandis; leaves of all three contained crystals which were shown to be Ca-rich in Pisonia. It is suggested that control of calcium levels may be particularly important in plants of highly calcareous coral cays. Predawn water potentials (&#936;) in Argusia, Pisonia and Melanthera averaged between - 0.3 and -0.8 MPa in wet weather, indicating high soil &#936; there was a daily fall of 0.5 - 1.O MPa in plant &#936;. During drought, predawn &#936; was lower in Argusia. Scaevola and Pisonia, and the daily &#936; fluctuation was small, presumably because of stomatal control of water loss. No evidence of osmotic adjustment was found in these three species. In Melanthera in drought, predawn &#936; became very low (often below -2.0 MPa) but the large daily fluctuation was still present, resulting in extremely low midday &#936;. From this and the large accumulation of solutes, especially at dry sites, it is suggested that Melanthera is capable of some osmotic adjustment. 
