Effects of nickel concentration in the nutrient solution on the nitrogen assimilation and growth of tomato seedlings in hydroponic culture supplied with urea or nitrate as the sole nitrogen source

Both the bene®cial and the adverse effects of nickel supplement on the N assimilation and growth of tomato plants were evaluated while either urea or nitrate was applied as the sole N source in the nutrient solution. The nickel concentration in the plant was related to that in the solution. Urea toxicity to the plants was reduced by the nickel supplement at 0.01 mg lÿ1, and no symptom of urea toxicity was observed in the plants when supplemented nickel was at 0.1 or 1 mg lÿ1. Both the plant growth and chlorophyll concentration in leaves of the urea-fed plants increased when nickel concentration in the solution was up to 0.1 mg lÿ1, but decreased by nickel at 1 mg lÿ1. The maximum growth of the urea-fed plants promoted by nickel supplement was still less than 80% of the nitrate-fed plants. Nickel supplement did not affect the growth of the nitrate-fed plants. The concentrations of leaf total-N in the urea-fed plants was enhanced by the nickel supplement, but was still lower than those in the nitrate-fed plants. At 0.1 mg lÿ1 nickel supplement, the concentrations of leaf urea-N and NH4-N in the urea-fed plants were about one-sixth and four times, respectively, of those without nickel supplement. Urea assimilation increased with the nickel supplement up to 0.1 mg lÿ1. No effect of nickel supplement on the N assimilation in the nitrate-fed plants was found. Nickel supplement up to 0.1 mg lÿ1 reduced urea toxicity and enhanced chlorophyll concentration, plant growth, and urea hydrolysis. The symptom of nickel toxicity and the Scientia Horticulturae 84 (2000) 265±273 * Corresponding author. Tel: ‡81-722-54-9421; fax: ‡81-722-54-9918. E-mail address: [email protected] (H. Ikeda). 0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 4 2 3 8 ( 9 9 ) 0 0 1 0 7 7 depression of plant growth were only observed with the nickel supplement up to 1 mg lÿ1. # 2000 Elsevier Science B.V. All rights reserved.