| Low temperature at vegetative stage inhibites tiller and biomass of rice,then affects rice yield,which is also related with nitrogen.It can be hypnotised that application of nitrogen might be an effective way to promote the growth recovery of rice after low temperature.However,there is still lacking data support for this research.With a water culture experiment,two rice varieties were selected for low temperature intensity(12°C and 15°C)and low temperature duration(5d,10 d and 15 d at 15°C),followed by nitrogen treatment after low temperature(40 mg/L and 80 mg/L)to verify the changes of tiller,dry matter accumulation and nitrogen uptake of rice,and clarify the effects of nitrogen application after low temperature on rice growth,nitrogen metabolism and antioxidant system,and then provide theoretical basis and guidance for reasonable nitrogen application under low temperature conditions.The main results are as follows:Low temperature inhibited the growth of rice during vegetative stage.During the vegetative stage of rice,15℃ inhibited the tillering development of sensitive varieties,and both varieties were inhibited at 12℃ low temperature.The effect of low temperature on tiller was also influenced by the duration of low temperature.The duration less than 5d at 15℃ did not affect the tiller of rice,but low temperature lasted longer than 10 d inhibited rice tiller number.In addition,15℃ low temperature inhibited the accumulation of dry matter and nitrogen,and changed with low temperature strength and duration.The longer low temperature lasted,the higher the MDA accumulated,and SOD activity was also affected by low temperature.Low temperature prolonged the growth period of rice.Compared with the normal temperature,the low temperature lasted for 5d,10 d,and 15 d delayed the rice leaf age by 0.6,1.2,and 1.4,respectively.After two weeks recovered to normal temperature,the leaf age difference between low temperature and normal temperature treatment was about 0.3,0.5 and 0.7,respectively,which was less affected by increasing nitrogen supply.Low temperature duration less than 5d did not affect the growth period of rice,but the duration longer than 10 d delayed the growth period for 3 to 6 days at the critical leaf-age of productive tillers.The application of nitrogen after low temperature improved the tiller recovery of rice.Under 15℃ condition,the tillers were restored to 87.90%-92.92% of the normal temperature after 4 weeks of nitrogen supply,and 70.39%-73.85% under 12℃ low temperature.For the sensitive varieties,the tillers could be recovered to normal level after increased nitrogen application at 10.5 leaf-age when low temperature lasted for less than 5d,which insensitive varieties could be recovered without increasing nitrogen.Even though the increase of nitrogen supply could promote tiller growth,the two varieties were unable to recover to normal levels when the duration longer than 10 d.The application of nitrogen after low temperature promoted aboveground dry matter accumulation of rice.After four weeks of nitrogen application,the aboveground dry weight of rice under low temperature treatment was still lower than normal temperature.Nitrogen application significantly increased the aboveground dry weight of sensitive varieties,which had no significant effect at 12°C.No matter short-term or long-term low temperature,there was no significant difference of the aboveground dry weight among all treatments at critical leaf-age of productive tillers.Nitrogen application after low temperature increased the aboveground dry weight,and significantly higher than normal level,which had little effect on root shoot ratio.The application of nitrogen after low temperature enhanced nitrogen uptake in rice.Nitrogen accumulation was affected little by nitrogen application at 12℃,which was significantly promoted at 15℃ with higher NR and GS activity.When low temperature lasted less than 5d,nitrogen application promoted nitrogen uptake of sensitive variety at the 10.5 leaf-age,which had little effect on insensitive varieties.Not only temperature sensitive variety but the insensitive variety,the nitrogen accumulation could recover to normal level when the duration longer than 10 d,and increased nitrogen application promoted nitrogen uptake significantly.In addition,the increased number of tillers was significantly positively correlated with the increase of nitrogen accumulation after nitrogen application(P<0.01).The application of nitrogen after low temperature alleviated the injure of MDA.After two weeks recovered to normal temperature,MDA content of two varieties was recovered to normal levels basically,and increasing nitrogen supply had little effect on MDA content.In addition,the damage of active oxygen of rice was disappeared in two weeks.SOD and POD activities could recover to normal levels when low temperatures duration less than 10 d,while POD activity was nearly recoverd when under lower temperatures or longer duration condition.Increasing of nitrogen application had significant effects on low temperature sensitive varieties.It can be seen that application of nitrogen after low temperature can promote the recovery of rice growth,but the promoting effect of nitrogen is related to low temperature intensity,low temperature duration,and varieties.In addition,low temperature delays the growth period of rice,which led to greater risks in production.and the increase of nitrogen supply did not affect the rice growth period.Therefore,it is necessary to choose the resistant varieties with shorter grow period in the low temperature year,and the environmental and economic benefits should be taken into consideration whether increase nitrogen supply or not. |
