THE RESPONSE TO SALINITY OF A POPULATION OF DACTYLOCTENIUM-AEGYPTIUM FROM A SALINE HABITAT IN SOUTHERN NIGERIA

The effects of salinity upon the growth, photosynthesis, ion and water contents of a population of Dactyloctenium aegyptium originating from a saline site in Nigeria were investigated. Growth was unaffected by a salinity of 10% artificial sea water, but was reduced by one third i n 20% and by two thirds in 30% artificial sea water respectively. Init ial adjustment to salinity was due both to increases in the concentrat ions of sodium and potassium per unit dry weight and to reduced hydrat ion, the latter being the more important at higher salinities. The inc rease in ion concentration in the cell sap balanced the salinity of th e medium at 10% artificial sea water, but was excessive at higher conc entrations of sea water. Net photosynthesis was unaffected by 10% arti ficial sea water but declined at higher salinities. The potassium cont ent of the plants did not fall below 200-250 mM, and the sodium to pot assium ratio did not exceed three, even at the highest salinities. Var iation in the concentration of nutrients (potassium, nitrate and sulph ate) in the medium in the presence of 23% artificial sea water had sig nificant effects upon growth, but these were small in relation to the inhibitory effect of the salinity. The reduction in growth could not b e attributed to lack of osmotic adjustment or to nutrient deficiency, and was probably due to ion toxicity within the leaves. The tolerance to reduced hydration, combined with the ability to germinate in saline conditions previously observed, could enable D. aegyptium to establis h in a saline soil. The population did not exhibit any halophytic char acteristics but did survive with a low growth rate at salinities up to 50% artificial sea water. It is concluded that the species was able t o colonize the saline site because of its inherent adaptability, rathe r than the possession of an ecotype adapted to saline conditions.