Abstract
Using two varieties, KR1 (salt-tolerant variety) and IR28 (salt-sensitive variety), relationship between Na+ uptake and transpiration under different humidity and salinity conditions was examined. The Na+ content of seedling increased more under lower humidity condition, and the tendency was sharper in IR28. The Na+ content changed with transpiration rate in both varieties. Transpiration stream concentration factor (TSCF), which denotes the ratio of ion concentration in the transpiration stream to that in the medium, decreased with the increase of transpiration rate. These results indicated that transpiration rate affected the filtration efficiency of roots in the Na+ uptake and transport to top. The lower TSCF of IR28 at the same transpiration rate suggested that the filtration efficiency was essentially higher in IR28. However, at the same NaCl concentration and air humidity condition, KR1 maintained comparatively higher transpiration rate, and consequently kept lower TSCF. It was supported with high leaf area ratio, high leaf water content and small stomatal resistance. These results indicated that the filtration efficiency in Na+ uptake depending on the transpiration rate under salinity condition was closely related to the difference of salinity tolerance between KR1 and IR28. It was suggested that plant characteristics on the filtration efficiency in Na+ uptake and the stability in water balance to environmental change might determine a passive Na+ uptake and transport to top under salinity condition.
