Effect of salinity on growth, photosynthesis and mineral composition in leguminous plantAlhagi pseudoalhagi(Bieb.)

Leguminous plant Alhagi pseudoalhagi was subjected to 0 (control), 50, 100, and 200 mM NaCI treatments during a 30 d period to examine the mechanism of tolerance to salinity. Plant dry weight, net CO2 assimilation rate, leaf stomatal conductance, intercellular CO2 concentration, and solute concentration in leaves, stems, and roots were determined. Total plant weight in the 50 mM treatment was 170% of that of the control after 10 d of treatment. Total plant weight was lower in the 100 and 200 mM treatments than in the control. The leaf CO2 assimilation rate was approximately 150% of that of the control in the 50 mM treatment, but was not affected significantly by 100 mM of NaCI, while it was reduced to about 60% of that the control in the 200 mM treatment. Similarly stomatal conductance was consistent with the CO2 assimilation rate regardless of the treatments. Intercellular CO2 concentration was lower in the NaCI-treated plants than in the control. Changes in CO2 assimilation rate due to salinity stress could be mainly associated with stomatal conductance and the carboxylation activity. Although the leaf Na+ concentration increased to 900 mmol kg-1 dry weight in the 200 mM treatment compared to 20 mmol kg-1 in the control, the plants did not die and continued to grow at such a high leaf Na+ concentration. Uptake and transportation rates of Na+, Ca2+, Mg2+, and K+, and the accumulation of N were promoted by 50 mM NaCI. Na+ uptake rate continued to increase in response to external NaCI concentration. However, the uptake and transportation rates of Ca2+, Mg2+, and K+ behaved differently under 100 and 200 mM salt stress. The results suggest that A. pseudoalhagi is markedly tolerant to salinity due mainly to its photosynthetic activity rather than to other physiological characteristics.