Sodium Concentration in Xylem Sap in Relation to Ion Exclusion, Accumulation and Secretion in Halophytes

Abstract

Salt secretion, salt accumulation and transpiration were simultaneously measured in salt-secreting and non-salt-secreting halophytes and glycophytes. The sodium content of the xylem sap was calculated. It is concluded that salt-secreting halophytes differ considerably in their sodium secretion rates, but less in their sodium exclusion capacity. Salt-sensitivity of the non-secreting species was related to a comparatively high sodium xylem content (15.1 mM Na). Transpiration rates are remarkably similar for all species. It is argued that the distinction between salt accumulators and salt excluders is not only based on differences in ion exclusion but is also related to the capacity to accumulate compatible osmotic solutes.In experiments aiming at an ecophysiological comparison of the mineral and water economy in relation to halophyte zonation, secretion, accumulation of sodium and transpiration were simultaneously measured in four salt-secreting and four non-salt-secreting halophytes and glycophytes. Plants were grown in a greenhouse (20°C, 65% RH; 6-18 hr light 7000Lux) in 0.25 strength Hoagland's solution with 0.2 M NaCI added. Salt secretion was measured by rinsing the leaves with distilled water over a 6 day period. Relative humidity of the air was kept at 65% in order to avoid the loss of secreted salt through run-off from the leaves,which occurs under more humid conditions (ROZEMA & RIPHAGEN 1977). Transpiration rates were determined by weight measurement for a 48 hr period. The total weight of the plants which were precultured for four weeks on NaCIfree0.25 strength Hoagland increased only slightly during the 6 day period. After harvesting and drying, the sodium content of the whole plant was determined by flame emission spectrophotometry. The sodium content of the xylem sap was calculated from the equation: . t ti I secretion + accumulation Ion concen ra IOn xy em sap = -----' ---------transpirationThe results are summarized in table 1, and it may be concluded that even the glycophytic species Juncus articulatus has the ability to exclude sodium ions to some extent since the rooting medium concentration (200 mM Na) is ten times reduced. In the non-secreting halophyte Juncus maritimus the sodium content of the xylem sap is even a factor 150 lower than that of the culture medium.Obviously the stronger exclusion of sodium ions in Juncus maritimus relates to its

Growth and ionic relations of fodderbeet and seabeet under saline environments

“…High Na + and Cl -ion accumulation by Beta spp. confirm the family Chenopodiaceae as salt accumulators (Rozema, et al, 1981). Presence of higher NaCl treatments increased Cl -ion accumulation in the root upto the third week.…”

SALT TOLERANCE IN THE HALOPHYTE SUAEDA MARITIMA (L.) DUM.

“…Xylem concentration was calculated by the method of Rozema et al (1981) as (rate of accumulation in shoot)/(rate of transpiration). The degree of ion X Calculated by the method of Pitman (1972).…”

“…Xylem concentration was calculated by the method of Rozema et al (1981) as (rate of accumulation in shoot)/(rate of transpiration). The degree of ion exclusion at the xylem was then expressed as the ratio between the xylem ion concentration (subscript x) and the external ion concentration (subscript o) x 100.…”

A Comparison of the Mineral Relations of a Halophytic Hemiparasite and Holoparasite

“…This low water potential of the hemiparasite and the continuous flow ofxylem water and dissolved nutrients is also related to a high transpiration rate of Odontites even during the dark period to some extent (ROZEMA et al 1985b). The above monocotyledonous host plants for Odontites were found to be salt-excluding (ROZEMA et al 1981) halophytes with relatively low Nalevels in the xylem sap. After growth in sand culture with 50 mM NaCl in the soil moisture the sodium content (mM) of the xylem sap in the hosts, obtained by the pressure bomb technique (ROZEMA et at.…”