Response of Tetragonia tetragonioides (Pallas) Kuntze to the combined effects of salts and nitrogen

摘要

The effect of nitrogen fertilization on the soil salt removing capacity of Tetragonia tetragonioides (Pallas) Kuntze, one of the best species for this purpose in arid conditions, was studied. An experiment was carried out with potted plants irrigated with water salinized with NaCl at 4 concentrations (0, 50, 100 e 200 mM), combined with 3 nitrogen forms, at constant molarity: 4 mM (NH{sub}4){sup}+; 2 mM (NH{sub}4){sup}+:2 mM (NO{sub}3){sup}-; 4 mM (NO{sub}3){sup}-. The combined effects of salts and nitrogen influenced the biomass production and its allocation to different plant organs, the mineral composition, the nutrient uptake and the crop quality. High salt concentrations did not reduced plant fresh weight, but there was a decrease of dry matter content and a change on plant biomass allocation, redirected towards the leaf. The reduction of the seed production by plants in saline conditions showed that the reproductive system was more susceptible than the vegetative system to salinity. The effect of salinity on fresh weight of leaves, and partly on stems and seeds of T. tetragonioides depended on the nitrogen source used. Excepting the control (0 mM NaCl), the best fresh weights were observed in the nitrogen source constituted by (NH{sub}4){sup}+/(NO{sub}3){sup}-, in contrast to the (NH{sub}4){sup}+ source, which induced the lowest weights independent on the salinity levels. There was no difference among treatments in nitrogen, magnesium and iron plant concentrations. The salinity level did not influence the potassium plant content. The presence of the ion nitrate in the irrigation solution increased the potassium content of the plant leaves. The phosphate and the calcium content of leaves decreased with salinity, but were unaffected by nitrogen source. The sodium and chloride leaf concentrations increased with the raising of the salinity level of the irrigation solution. The concentration of these ions was not influenced by the nitrogen treatments.