Effects of seed nickel reserves or externally supplied nickel on the growth,nitrogen metabolites and nitrogen use efficiency of urea- or nitrate-fed soybean

Background and aims

Nickel (Ni) has a critical role in the urea metabolism of plants. This study investigated the impact of seed Ni content along with external Ni supply on the growth, various nitrogen (N) metabolites and N use efficiency (NUE) of soybean plants.

Methods

Soybean plants raised from Ni-poor or Ni-rich seeds were grown in nutrient solution with or without external Ni supply and fed with either urea or nitrate as the sole N source. The changes in growth, leaf chlorophyll levels, Ni and N concentrations of different plant parts, tissue accumulation of various N metabolites and N uptake of soybean as well as NUE and its components were examined.

Results

Nickel starvation reduced the shoot biomass of urea-fed plants by 25 % and the leaf chlorophyll levels by up to 35 %, but nitrate-fed plants were unaffected. Visual toxicity symptoms were not observed in urea-fed plants. Under urea supply, Ni-deficient plants had lower levels of total N, protein and free amino acids in various organs. Root uptake of urea was severely depressed in Ni-deprived plants. Availability of Ni did not have any effect on the NUE of nitrate-fed plants, whereas its deficiency reduced the NUE of urea-fed plants by 30 %. The growth and N nutritional status of urea-fed soybean were significantly improved by high seed Ni reserves as well as external Ni supply.

Conclusion

Adequate Ni supply is required for maximizing the growth, root uptake of urea and NUE of urea-fed plants. Seed Ni reserves contribute significantly to the Ni and thus N nutritional status of soybean.