The ability of the more important pasture and fodder plants grown in New Zealand to translocate sodium from their root systems into their leaf tissue was examined in a glasshouse pot experiment. Plants were classified into two distinct types: natrophilic plants, which have the capacity to accumulate large amounts of sodium in their shoots where adequate quilntities of sodium are present in the growth medium, but have low concentrations in their roots~ and natrophobic plants for which the converse is generally true. A further subdivision was made within both types, depending on the concentration of sodium in the lower stem or stubble tissue. The importance of this classification is discussed in relation to a nutritional problem which arises where natrophobic plants form a substantial part of the diet of grazing animals.

The effect of increasing concentrations of sodium chloride in the root zone on growth, chemical composition and nitrate reductase activity of perennial ryegrass and timothy was investigated in a glasshouse pot experiment. For ryegrass, a natrophile, sodium chloride had little effect on growth, whereas for timothy, a natrophobe, growth was severely depressed by comparatively low concentrations of salt. The result also indicate that translocation of sodium into the leaves of timothy took place readily only after the accumulation sites in the roots and lower stems had been saturated with this element. This means that relatively large quantities of sodium chloride were needed to produce concentrations of sodium in the leaves of timothy as high as those normally found in the leaves of ryegrass. Sodium chloride increased the uptake of total and nitrate‐nitrogen but, in contrast, depressed the uptake of potassium by ryegrass and timothy It was therefore concluded that the marked stimulation by sodium chloride of nitrate reductase activity in both species was more the result of the increased uptake of nitrates than a specific effect of this salt on the enzyme. The practical implications of these results are discussed.

A study of transpiration rates, and of uptake and translocation of sodium and potassium, has supported a previous classification made for certain pasture and fodder species. The plants termed natrophiles were found to have relatively high transpiration rates and to translocate relatively large amounts of absorbed sodium from root systems into leaves. Plants termed natrophobes had lower transpiration rates and translocated less sodium from roots to leaves. In contrast, potassium was readily translocated by both natrophiles and natrophobes; consequently, compared with natrophobes, natrophiles had low K/Na ratios in their leaves. In general, transpiration rate was less associated with absorption of sodium by roots than with translocation of sodium from roots to aerial parts. The practical and ecological implications of these results are discussed.

SUMMARY Maximum potassium uptake is achieved by beech mycorrhizas from concentrations of chloride of about 0.2 mM. Addition of NaCl up to 0.5 mM does not significantly reduce K+ uptake from 0.1 mM chloride solutions, although the KCl significantly reduces Na+ uptake. Potassium is rapidly lost from mycorrhizal tissues at temperatures above 20° C, but only after some delay from tissues at lower temperatures. Addition of calcium ions (up to 1.0 mM CaCl2) does not significantly affect potassium uptake or loss. CaCl2 added to RbCl solutions slightly reduces Rb+ uptake. Losses of K+ from mycorrhizal tissues at temperatures above 20°C may be prevented by the application of glucose or fructose. Neither the process of carbohydrate uptake nor the increased internal concentration of carbohydrate itself is responsible for the reduction in potassium loss. It seems probably that factors bringing about the retention of potassium are generated in carbohydrate metabolism. The potassium loss engendered by high osmotic pressure of the external solution seems to be a separate phenomenon from that which occurs at high temperatures.

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