To investigate the effects of Ca 2+ on cation accumulation and K + /Na + selectivity, in this study, two-week-old rice (Oryza sativa L.) plants were exposed to 25 or 125 mmol/L NaCl with or without 10 mmol/L CaCl 2 . At low salinity (25 mmol/L NaCl), Ca 2+ significantly decreased Na + accumulation in roots, increased K + accumulation in shoots, and maintained higher K + /Na + ratios in both roots and shoots of rice plants. At high salinity (125 mmol/L NaCl), however, Ca 2+ did not have any effects on Na + , K + accumulation and K + /Na + ratios in plants. Further analysis showed that, at low salinity, the addition of Ca 2+ significantly enhanced the selective absorption and transport capacity for K + over Na + in rice. Although Na + efflux and Na + influx were remarkably reduced by Ca 2+ under both low and high salt stresses, their ratio was lowered only under low salt stress. In summary, these results suggest that Ca 2+ could regulate K + /Na + homeostasis in rice at low salinity by enhancing the selectivity for K + over Na + , reducing the Na + influx and efflux, and lowering the futile cycling of Na + .

A silicon (Si)-deficient top soil was used in a pot experiment to investigate the effect of Si application on the shoot and root morphology of alfalfa (Medicago sativa L.). Silicon was applied to the alfalfa plants at 6 different rates (0, 0.025, 0.05, 0.10, 0.20, 0.30 g/kg), and each treatment was replicated 6 times. This study indicated that the Si content of roots and shoots increased significantly (P<0.05) with increasing Si concentration in the soil, and that the Si content of roots was greater than that of shoots. Plants treated with Si had increased leaf area, height, forage yield and shoots per plant during the reproductive period in comparison with controls. The application of Si also increased root volume, the number of secondary roots and root biomass. The effects of Si application were greater on roots than on shoots. The ratio of shoot to root dry weight was below 1.62 when Si was applied to plants and 1.91 without Si application. Overall, overcoming available Si deficiency resulted in a significant increase in shoot and root growth.