THE GROWTH AND MINERAL COMPOSITION OF THREE SPECIES OF SPERGULARIA AS AFFECTED BY SALINITY AND NUTRIENTS AT HIGH SALINITY

The effects of salinity on the growth of three species of Spergularia and the effects of some levels of different nutrients on the growth and mineral composition of the three species under high salinity were investigated in sand culture. In response to the effects of salinity, S. marina and S. rupicola behaved like true halophytes in terms of survival, mean dry weight and plant part weight ratios. Spergularia rubra also behaved like an ecological halophyte in terms of dry weight but in terms of survival, it behaved like a glycophyte. The poor growth exhibited by the halophytes, S. marina and S. rupicola under high salinity condition was significantly reversed withthe addition of most nutrients, while theglycophyte, S. rubra showed no favorable response, rather the combination of some nutrients further reduced its growth. The increased growth in S. marina was as a result of increased root growth while in S. rupicola it was as a result of increased root and stem growth. High salinity conditions resulted in a marked reduction in calcium and potassium content and an increase in sodium and chloride content of leaves of the species. Addition of many of the nutrients to plants under high salinity condition generally resulted in increased sodium, calcium, potassium, and magnesium content of leaves, except that the addition of phosphate resulted in decreased amounts of calcium and magnesium. Results are discussed in relation to the salt tolerance of the species and how the supply of nutrients to these species in their natural habitats might help them overcome high salinity problems. MUCH IS NOW KNOWN about the effects of salinity on plant growth. Glycophytes generally achieve their best growth in non-saline conditions and growth is reduced as salinity is increased. On the other hand, halophytes achieve their best growth at varying levels of salinity depending on their degree of salt tolerance, although their growth also is retarded at high salinities (Ashby and Beadle, 1957; Greenway, 1968; Waisel, 1972; Ungar, 1974; Okusanya, 1979b). Levitt (1980) reviewed various theories put forward to explain the causes of reduced growth in plants at high salinity. One of these is the 1 Received for publication 25 April 1983; revision accepted 15 November 1983. We would like to thank the Morton Salt Company for permission to carry out experiment on their property at Rittman, Ohio, the Director of Jardin Botanique, Nantes, for the supply of seeds, and Dr. A. J. C. Malloch for his comments on the manuscript. O.T.O. would like to thank the University of Lagos for support and permission to take up a Visiting Professorship post at Ohio University, Athens, during which time this work was carried out. I.A.U. would like to thank the National Science Foundation for research grant No. DEB 79-27236. Much thanks are also due to Mrs. I. T. Okusanya, Mrs. Daleen Dotson, Ms. Betty Moore, Mr. M. A. Adesi and Dr. R. B. Rypma for their help. 2Permanent address: Department of Biological Sciences, University of Lagos, Yaba-Lagos, Nigeria. 3 To whom reprint requests should be addressed. inability of the roots to absorb nutrients due to competition with sodium ions in the medium (Solov'ev, 1969). In nature and in the various laboratory salinity experiments carried out with halophytes, there are usually adequate levels of nutrients in the medium even at high salinities, but many species still show signs of mineral deficiency (Zhukovskaya, 1962; Solov'ev, 1969; Pigott, 1969; Okusanya, 1979b). It thus appears that the above theory is true. Even though much attention has been focused on the mechanism of salt tolerance in halopytes (StewartandLee,1974;Weimberg,Lernerand PoljakoS-Mayber, 1982), what has not been determined, especially for many halophytes, is whether an increase in the levels of nutrients in the medium would result in a corresponding increase in the uptake of nutrients which could lead to amelioration of the high salinity effects. The problems of high soil salinity is understandably being vigorously pursued in the agricultural field, but, in contrast, not much work has been done with halopytes, which are the natural inhabitants of saline environments. However, field studies on the effiects of mineral nutrients on the growth of halopytes are now being pursued (Hoffman and Sachert, 1967; Patrick and Delaune, 1976; Jeffieries, 1977; Haines, 1979; Smart and Barko, 1980; and Loveland and Ungar, 1983), but laboratory