Effects of Molybdenum, Nickel, and Nitrogen Sources on the Mineral Nutrition and Growth of Rice Plants

Abstract

Upland rice plants, cultivar ‘IAC 202,’ were grown in nutrient solution until full tillering. Treatments consisted of ammonium nitrate (AN) or urea (UR) as nitrogen (N) source plus molybdenum (Mo) and/or nickel (Ni): AN + Mo + Ni, AN + Mo − Ni, AN − Mo + Ni, UR + Mo + Ni, UR + Mo − Ni, and UR − Mo + Ni. The experiment was carried out to better understand the effect of these treatments on dry‐matter yield, chlorophyll, net photosynthesis rate, nitrate (NO₃ ⁻‐N), total N, in vitro activities of urease and nitrate reductase (NR), and Mo and Ni concentrations. In UR‐grown plants, Mo and Ni addition increased yield of dry matter. Regardless of the N source, chlorophyll concentration and net photosynthesis rate were reduced when Mo or Ni were omitted, although not always significantly. The omission of either Mo or Ni led to a decrease in urease activity, independent of N source. Nitrate reductase activity increased in nutrient solutions without Mo, although NO₃ ⁻‐N increased. There was not a consistent variation in total N concentration. Molybdenum and Ni concentration in roots and shoots were influenced by their supply in the nutrient solution. Molybdenum concentration was not influenced by N sources, whereas Ni content in both root and shoots was greater in ammonium nitrate–grown plants. In conclusion, it can be hypothesized that there is a relationship between Mo and Ni acting on photosynthesis, although is an indirect one. This is the first evidence for a beneficial effect of Mo and Ni interaction on plant growth.

Keywords:

• Chlorophyll
• micronutrients
• nitrate reductase
• photosynthesis
• plant nutrition
• urease

ACKNOWLEDGMENTS

We thank Dr. Jonathan J. Hart (USDA‐ARS/Cornell University) for his valuable comments on the manuscript and also our colleagues Saulo de Tarso Aidar and Daniel Manfredini for their assistance in the plant analyses. This work was supported by fellowships awarded from the National Council for Scientific and Technological Development (CNPq), Sao Paulo Research Foundation (FAPESP), and Coordination of the Perfecting of Personnel of Higher Level (CAPES).

Notes

This article is dedicated to the memory of Prof. Eurípedes Malavolta; his example and passion for teaching will always be remembered.