Growth and physiological responses of balansa clover and burr medic to low levels of salinity

This study investigated a wide range of morphological and physiological responses of burr medic ( Medicago polymorpha L. cv. Scimitar) and balansa clover ( Trifolium michelianum L. cv. Frontier) to different levels of salinity. Balansa clover and burr medic plants were grown in the greenhouse at 25°C day temperature and 16°C night temperature. Salt treatments were applied 6 weeks after germination, and plants were grown for a further 6 weeks before harvest. The salt treatments included a control, 20 m m , 40 m m , and 80 m m of NaCl. The shoot biomass yield was significantly affected by the species × salt interaction ( P = 0.04). For balansa clover, the shoot biomass yield was greatest for the control treatment and lowest for the 20 m m NaCl treatment. For burr medic, the shoot biomass yield did not differ among salt treatments. Sodium (Na + ) and potassium (K + ) concentrations in leaves and stems increased with salinity. Compared with a non-saline control, sodium concentration in leaves in the 80 m m NaCl treatment was 3-fold higher for balansa clover and 2-fold higher for burr medic. Under various saline treatments, leaf Na + /K + ratio stayed relatively constant in balansa clover (0.3–0.4) and burr medic (0.4–0.5), whereas stem Na + /K + ratios for both species increased with salinity. The most sensitive parameters to salinity were Na + /K + and Na + /Ca 2+ ratios, whereas biomass, chlorophyll fluorescence, net photosynthesis, stomatal conductance, transpiration, and δ 13 C and δ 15 N discrimination were least sensitive. Therefore, accumulation of sodium in the plant tissues did not reach the threshold for causing reduction in growth.