Seasonal changes in sodium and chloride concentration of saltbush (Atriplex spp.) leaves as related to soil and plant water potential

Abstract

Sodium and chloride concentrations in mature leaves of two Atriplex species, A. nummularia and A. vesicaria, growing on two clay soils were monitored during June 1969 to June 1970. The corresponding soil water content (W-), osmotic potential (π) and matric potential (τ) of soil water, and relative leaf water content (w) were also evaluated.

Both the sodium and chloride concentrations in leaves increased progressively with the corresponding decrease in W from September to December, reaching about twice their original values. From December on, sodium and chloride remained relatively stable until April when they started to decline progressively with a steady increase in W.

Intermittent rains during summer changed W for short periods, but the leaf salinity remained unchanged. Irrespective of soil, A. nummularia leaves contained more sodium than A. vesicaria, while the reverse was true for chloride.

Invariably leaf salinity was strongly correlated with W, τ and π but the correlation with w was significant only for A. vesicaria. Empirical equations fitted to indicate the relation of sodium and chloride to each of the variables and also to multiple regressions of (π τ) and (W, w) are given.

Various factors which might be responsible for inducing seasonal variability in the leaf salinity are discussed. It appears that the higher salinity build-up in Atriplex during summer is not only due to increased electrolyte concentration in the growing medium and to high transpiration rates, but is also associated with drought tolerance by these plants.