Sodium tolerance of plants in relation to ionic balance and the absorption ability of microelements

Abstract

Salinity stress is a major abiotic problem in arid land agriculture. In particular, Na stress severely limits crop production because it causes Na toxicity and disturbs the homeostasis of essential cations and microelements in crops. The purpose of the present study was to verify the validity of two indexes with regard to Na tolerance in plants: (1) cation balance (([K]+[Ca]+[Mg])/[Na]), (2) absorption ability of microelements. Salicornia bigelobii (highly salt tolerant), beet (tolerant), maize (moderately sensitive) and bean (sensitive) were grown in artificially prepared saline (SA), sodic (SO) and highly sodic (HSO) soils. Salicornia bigelobii showed the best growth in SO soil and accumulated Na in the growing part of the shoot. Beet showed the best growth in SA soil and also needed Na for satisfactory growth. Both species, therefore, can be classified as halophytes. There was no relationship between growth and cation balance in Salicornia bigelobii and beet. The salt treatments suppressed the growth of maize and bean, with more severe suppression in bean. The cation balance of maize was higher than that of bean. Cation balance can, therefore, be an index of Na tolerance in maize and bean, which are glycophytes. Salicornia bigelovii and beet actively absorbed microelements under high Na conditions. In maize and bean, the salt treatments lowered the uptake amount of microelements, more so in bean. Absorption ability of microelements can, therefore, be an index of Na tolerance, irrespective of whether the plants are halophytes or glycophytes.