Effect of salinity and planting density on physiological responses of Allenrolfea occidentalis

Physiological responses of Allenrolfea occidentalis to salinity and seedlin g density were investigated. Effects of salinity (0, 200, 400, 600, 800, an d 1000 mM NaCl) and 3 planting densities (2000, 4000, 6000 plants m(-2)) on the growth, survival, and ecophysiology of A. occidentalis, a stern succul ent inland halophyte, were studied under controlled greenhouse conditions. Plants were grown in a sand culture using subirrigation. Dry mass of roots was highest at 600 mM NaCl at low density (2000 plants m(-2)), but declined as salinity increased. Tissue water content was highest at the 200 mM NaCl treatment and decreased with increased salinity. Water potential of the pl ants became more negative with increasing salinity due to the accumulation of NaCl in the leaves. Inorganic ions, especially Na+ and Cl-, contributed substantially to dry mass. Na+ and Cl- concentration in shoots and roots in creased when NaCl level was increased while K+, Ca++, Mg++, SO4-, and NO3 c ontents decreased. Net photosynthesis increased at low salinity (200 mM), b ut photosynthesis at other salinities was not significantly different from the control. While A. occidentalis is very salt tolerant and photosynthesis functioned reasonably well at high salinities, extremely high salinity did decrease dry mass of roots and shoots.