Nitrogen application after low-temperature exposure alleviates tiller decrease in rice

Abstract

Low temperature during the vegetative stage depresses the rice tillering, which decreases rice yield. The production and development of rice tillers can be closely related to the presence of nitrogen. Therefore, supplying rice with nitrogen after exposure to low temperatures may be an effective method to promote rice tillering. However, there is limited research about the effects of nitrogen application after low-temperature exposure on rice tillering. Water culture and field experiments were conducted using two rice varieties in each experiment; three temperatures (12 °C, 15 °C and 18 °C) and temperature durations (5, 10 and 15 days under 15 °C) were set in water culture experiments, and two temperatures (approximately 13 °C and 17 °C) were set in the field experiment. Two (40 mg N L−1 and 80 mg N L−1) and four (0, 20, 40 and 80 kg N ha−1) nitrogen levels after temperature treatment were applied in the water culture and field experiments, respectively. The results showed that low temperatures decreased rice tillering, nitrogen accumulation and yield, and higher stress strengths or longer low temperature durations led to greater tiller suppression. Nitrogen application after low-temperature stress enhanced the recovery of rice tillering. Four weeks after nitrogen application, the rice tiller number recovered to 87.90–92.92% of normal levels under 15 °C and to 70.39–73.85% of normal levels under 12 °C. Tillering in sensitive rice could be recovered to levels found at normal temperatures at the 10.5-leaf stage with increased nitrogen application after 5 days at 15 °C, whereas insensitive rice could be recovered without increased nitrogen. When low-temperature stress lasted for more than 10 days, increasing nitrogen application improved rice growth as well, although neither variety’s tillering recovered to normal levels. The correlation analysis also showed that the increase in tiller number was closely related to the increase in nitrogen accumulation (P < 0.01). Moreover, increasing the nitrogen application after low temperatures increased the rice nitrate reductase (NR) and glutamine synthase (GS) activities and nitrogen accumulation. The field experiment also showed that increasing the nitrogen application after low temperature could help rice yield recovery, but applying excessive nitrogen (more than 40 kg N ha-1 in this experiment) resulted in yield and nitrogen loss. These results highlighted the positive effects of nitrogen on rice growth recovery after low-temperature stress, which was affected by low temperature strength, duration and rice variety.