
TY  - JOUR
A1  - Allaway, WG 
A1  - Pitman, MG 
A1  - Storey, R 
A1  - Tyerman, S 
A1  - Ashford, AE 
T1  - Water Relations of Coral Cay Vegetation on the Great Barrier Reef: Water Potentials and Osmotic Content
JF  - Australian Journal of Botany
JO  - Aust. J. Bot.
Y1  - 1984
VL  - 32
IS  - 5
SP  - 449
EP  - 464
KW  - 
UR  - https://doi.org/10.1071/BT9840449 
N2  - 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. 
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