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Growth stage modulates salinity tolerance of New Zealand spiach (Tetragonia tetragonioides, Pall.) and red orach (Atriplex hortensis L.)

Wilson, C., Lesch, S.M., Grieve, C.M.
Annals of botany 2000 v.85 no.4 pp. 501-509
Tetragonia tetragonoides, Atriplex hortensis, developmental stages, salinity, salt tolerance, nutrient solutions, planting date, electrical conductivity, magnesium sulfate, sodium sulfate, sodium chloride, calcium chloride, osmosis, seedlings, pH, crop yield, species differences, biomass production
The response of two speciality vegetable crops, New Zealand spinach (Tetragonia tetragonioides Pall.) and red orach (Atriplex hortensis L.), to salt application at three growth stages was investigated. Plants were grown with a base nutrient solution in outdoor sand cultures and salinized at 13 (early), 26 (mid), and 42 (late) d after planting (DAP). For the treatment salt concentrations, we used a salinity composition that would occur in a typical soil in the San Joaquin Valley of California using drainage waters for irrigation. Salinity treatments measuring electrical conductivities (ECi) of 3, 7, 11, 15, 19 and 23 dS m−1were achieved by adding MgSO4, Na2SO4, NaCl and CaCl2to the base nutrient solution. These salts were added to the base nutrient solution incrementally over a 5-d period to avoid osmotic shock to the seedlings. The base nutrient solution without added salts served as the non-saline control (3 dS m−1). Solution pH was uncontrolled and ranged from 7.7 to 8.0. Both species were salt sensitive at the early seedling stage and became more salt tolerant as time to salinization increased. For New Zealand spinach, the salinity levels that gave maximal yields (Cmax) were 0, 0 and 3.1 dS m−1and those resulting in a 50% reduction of biomass production (C50) were 9.1, 11.1 and 17.4 dS m−1for early, mid and late salinization dates, respectively. Maximal yield of red orach increased from 4.2 to 10.9 to 13.7 dS m−1as the time of salinization increased from 13, to 26, to 42 DAP, respectively. The C50value for red orach was unaffected by time of salt imposition (25 dS m−1). Both species exhibited high Na+accumulation even at low salinity levels. Examination of K-Na selectivity data indicated that K+selectivity increased in both species with increasing salinity. However, increased K-Na selectivity did not explain the increased salt tolerance observed by later salinization. Higher Na-Ca selectivity was determined at 3 dS m−1in New Zealand spinach plants treated with early- and mid-salinization plants relative to those exposed to late salinization. This corresponded with lower Cmaxand C50values for those plants. Lower Ca uptake selectivity or lower Ca levels may have inhibited growth in young seedlings. This conclusion is supported by similar results with red orach. High Na-Ca selectivity found only in the early-salinization plants of red orach corresponded to the lower Cmaxvalues measured for those plants.