Osmotic Relations of Some Plants of the Northern Marshall Islands

Osmotic relations of several strand species were investigated by determining osmotic potentials and sodium contents of leaf samples collected in the field, by measuring the electrical conductivity of groundwaters and soil solutions, and by growing seedlings in the greenhouse in culture solutions with varying levels of added salt. Mean of the field-collected leaves ranged from - 1.9 to - 3.1 M Pascals, compared with that of seawater at - 2.7 M Pa. Sodium contents of the leaves were high, commonly being 1 to 3% of the dry weight. Groundwaters mostly ranged in electrical conductivity from 16 to 50 mmhos/cm (equal to about 0.86 to 2.7 M Pa). In culture solutions, seedlings of four shrubby species (Cordia subcordata Lam., Guettarda speciosa L., Scaevola sericea Vahl, and Tournefortia argentea L.f.) and a native variety of squash (Cucurbita pepo L.) all grew well at solution of -0.28 M Pa, but were depressed to about 50% yield at -0.42 M Pa . The woody species declined to about 10-20% yield at - 1.4 M Pa, and grew only a little at - 2.8 M Pa (a solution equal in to that of seawater)