Studies in Eco-physiology of Dactyloctenium Aegyptium L., Oryza Sativa L. and Porteresia Coarctata(Tateoka)
The Salinity tolerance of the grass Dactyloctenium aeqyptium was compared with that of two tropical rice cultivars (Oryza sativa) KAU 2 and HG 2153 and a closely related temperate member of the gramineae, Porteresia coarctata. Experiments were also carried out to determine the tolerance mechanism of D.aeqyptium with a view to making recommendations as to its use as a biological soil desalinizer and reclamation species in Nigeria. The effects of varying the levels of potassium, nitrate and sulphate in the culture solution on the growth, mineral composition and ion relations at 10 and 25% sea water concentrations were investigated in D. aeqyptium to determine how the supply of these nutrients to this species in their natural habitats might help them overcome high salinity problems. The photosynthetic ability, stomatal conductance to water and carbon dioxide and transpiration at different salinity regimes were also investigated in D. aeqyptium to find out the physiological basis for the effect of salinity on its growth. The germination ecology of D. aeqyptium was further investigated to find out the response of the plant to such ecological factors like light and dark regimes, Ph., salinity, soil types, soil moisture and temperature. Based on the response of the four species tested to salinity, the species can be divided into two main groups namely, those that have their growth supported as sea water concentration increased, that is, the two rice varieties, and those that are either not affected in growth or have insignificant stimulation of growth (dry weight) at low salinity that is P. coarctata and D. aeqyptium respectively. P. coarctata appears to be the most tolerant species followed by D. aeqyptium, the rice cultivar, KAU 2, and the least tolerant being the other rice cultivar HG 2153. P. coarctata accumulated relatively less Na + and C1 – in their shoots and maintained the lowest Na: K ratio at 30% sea water concentration compared with the other species. In D. aeqyptium the use of half of the level of potassium, twice the level of nitrate and half of the level of nitrate in the culture solution resulted in significant stimulation of dry weight at 10% sea water and amelioration of poor growth at 25% sea water concentration. However the use of double the level of potassium or half or double the level of sulphate in the culture solution depressed growth significantly at both concentrations of sea water. At half the level of potassium or nitrate or double the level of nitrate, reduced uptake of sodium and chloride ions, increased water uptake and plant succulence, increased sugar concentration and increase osmolarity.