Effect of increasing zinc application on rice nitrogen metabolism and dry matter accumulation under low temperature stress

  Objectives  Zinc (Zn) has been proved of enhancing rice growth and resistance to low temperature stress. We studied the potential of increasing Zn supply to alleviate low temperature damage on rice during vegetative period.

  Methods  A hydroponic culture experiment was conducted using 3-leaves-1-heart leaf rice seedlings inside growth chamber. ZnSO₄·7H₂O concentrations of 0.08, 0.15, and 0.30 μmol/L were set up to represent low, conventional and high Zn application levels. When the rice seedlings grew to 5 leaves-1-heart leaf stage, they were subjected to low and regular temperatures (12℃ and 20℃) for 7 days, then harvested for analysis of dry matter, Zn and N content, root vitality, and indexes of N metabolism.

  Results  Compared to regular temperature, low temperature significantly reduced the total and active absorption area and oxidizing ability of rice root, decreased N and Zn uptake, and then decreased rice tiller number by 22.86% (P < 0.05), shoot and root dry matter by 33.60% (P < 0.05) and 28.42% (P < 0.05), respectively. Under low temperature, high Zn treatment significantly increased the total and active absorption area, and oxidizing capacity of root, although the rice tillering and shoot dry matter under high Zn treatment were not as high as regular temperature, but were significantly higher than the conventional Zn treatment. Compared with conventional Zn treatment, high Zn under low temperature significantly increased Zn concentration, the nitrate reductase (NR) and glutamine synthetase (GS) activities, the shoot and root N accumulation. Meanwhile, high Zn increased the rice leaf antioxidant enzymes activities and decreased the malondialdehyde concentration by 26.39% (P < 0.05). Under low temperature, rice root Zn concentration decreased significantly, the GS activity and N concentration decreased by 17.65% and 4.78% (P < 0.05), respectively.

  Conclusions  Increasing Zn supply level during rice seedling stage could increase the root vigor, improve Zn absorption, enhance N metabolism, and then promote nutrients and dry matter accumulation, thus effectively alleviate the possible low temperature damage happened in vegetative stages.