| Water is crucial for the growth and development of rice,and different irrigation methods have a significant impact on rice growth and yield.The tillering stage is a critical period for rice growth and also has water-saving potential.Therefore,studying the effects of different irrigation methods during the tillering stage on rice metabolism is of great importance.In this experiment,Dongnong427 and Longdao 18 were used as materials,employing a split-plot design with irrigation methods as the main plots and varieties as the subplots.Four treatments were set,including continuous flooding during the tillering stage(T1),light-dry-wet alternate irrigation during the critical leaf age for effective tillering(T2),sunlight exposure during the critical leaf age for effective tillering(T3),and light-dry-wet alternate irrigation throughout the tillering stage(T4).The study aimed to investigate the effects of different irrigation methods during the tillering stage on nitrogen accumulation,transport,and distribution,key nitrogen metabolism enzyme activity,root injury intensity,amino acid content in injury exudate(total amino acids,glutamic acid,and glutamine),grain protein content and composition,yield,and water use efficiency in cold-tolerant japonica rice.The objective was to determine the most suitable irrigation method during the tillering stage and provide a theoretical basis for water-saving cultivation practices for cold-tolerant japonica rice.The main results of this study are as follows:(1)The nitrogen accumulation in Dongnong 427 and Longdao 18 plants gradually increased with the progression of growth.The nitrogen accumulation under the T2 and T3 treatments was significantly higher than the T1 treatment,while the T4 treatment was significantly lower than the T1 treatment,with no significant difference between the T2 and T3 treatments.The proportion of nitrogen allocation to the roots showed no significant difference among treatments at each growth stage.At the maturity stage,the proportion of nitrogen allocation to the leaves under the T1 treatment was significantly higher than the T3 and T4 treatments,with no significant difference compared to the T2 treatment.The proportion of nitrogen allocation to the stem sheaths reached its peak after the heading stage and gradually decreased.The T1 treatment was significantly higher than other treatments,while the T2 and T3 treatments were significantly higher than the T4 treatment,with no significant difference between the T2 and T3 treatments.The proportion of nitrogen allocation to the panicles under the T4 treatment was significantly higher than other treatments at the maturity stage.The nutrient organ nitrogen output rate under the T4 treatment was significantly higher than other treatments,and the nitrogen transport contribution rate in nutrient organs under the T3 treatment was significantly higher than other treatments.The rice grain production efficiency under the T1 treatment was significantly higher than other treatments.(2)The activities of nitrate reductase(NR),glutamine synthetase(GS),glutamate synthase(GOGAT),and glutamate dehydrogenase(GDH)in functional leaves of both varieties showed the following pattern at each growth stage: T2 > T3 > T1 > T4.The T2 treatment exhibited significantly higher activity than the other treatments,while the T4 treatment showed significantly lower activity than the other treatments.The activities of GS,GOGAT,and GDH in grains increased initially after flowering and then decreased.GS and GOGAT activities reached their peak 10 days after flowering,while GDH activity reached its peak 20 days after flowering.The activities of GS,GOGAT,and GDH in grains under the T2 and T3 treatments were significantly higher than those under the T1 and T4 treatments.The T4 treatment exhibited significantly lower activity than the T1 treatment,with no significant difference between the T2 and T3 treatments.Under the T1,T2,and T3 treatments,the activities of nitrogen metabolism key enzymes in functional leaves and grains of Longdao 18 were significantly higher than those of Dongnong 427.(3)The root injury intensity,total amino acid content,as well as glutamine and glutamate content in injury exudate gradually decreased after the heading stage in both varieties.The root injury intensity and total amino acid content showed the following pattern: T2 > T3 > T1 > T4,with significant differences among the treatments.The levels of glutamine and glutamate in injury exudate were significantly higher under the T2 treatment compared to the T1 treatment,with the lowest levels under the T4 treatment.For Dongnong 427,the glutamine and glutamate content under the T3 treatment was significantly lower than the T2 treatment,while the glutamine content was significantly higher than the T1 treatment,and there was no significant difference in glutamate content compared to the T1 treatment.For Longdao 18,the glutamine content under the T3 treatment was significantly lower than the T2 treatment,with no significant difference compared to the T1 treatment,while the glutamate content showed no significant difference compared to the T2 treatment and was significantly higher than the T1 treatment.The root injury intensity and total amino acid content in Longdao 18 were significantly higher than those in Dongnong 427.(4)The content of strong and weak-grain proteins under the T2 treatment was significantly higher than that under the T1 treatment,while the T4 treatment showed significantly lower content than the T1 treatment.The content of strong-grain proteins under the T3 treatment was significantly lower than that under the T2 treatment,with no significant difference for weak-grain proteins compared to the T2 treatment.The content of albumins,globulins,and glutelins in strong and weak grains under the T2 treatment was significantly higher than that under the other treatments.For Dongnong 427,there was no significant difference in the content of albumins in strong and weak grains between the T3 treatment and the T1 treatment,while for Longdao 18,the T3 treatment showed a significant increase compared to the T1 treatment.There was no significant difference in the content of globulins in strong and weak grains of Dongnong 427 among the treatments,and for Longdao 18,there was no significant difference among the T1,T2,and T3 treatments,but all of them were significantly higher than the T4 treatment.The content of alcohol-soluble proteins in strong and weak grains under the T4 treatment was significantly lower than that under the other treatments.For Dongnong 427,the content of alcohol-soluble proteins in strong and weak grains under the T2 treatment was significantly higher than that under the other treatments,with no significant difference between the T1 and T3 treatments.For Longdao 18,there was no significant difference among the T1,T2,and T3 treatments.The content of glutelins in strong and weak grains under the T2 treatment was significantly higher than that under the other treatments.The reduction in the content of proteins,globulins,and glutelins in strong and weak grains under the T4 treatment was significantly higher in Longdao 18 compared to Dongnong 427 under the T1 treatment.(5)Under the T2 treatment,the aboveground dry weight of both varieties did not show a significant difference compared to the T1 treatment during the heading to maturity stage,but it was significantly higher than the T3 and T4 treatments.The root dry weight under the T4 treatment was significantly lower than the other treatments,while the root dry weight under the T2 and T3 treatments did not show a significant difference compared to the T1 treatment at each growth stage.The root-shoot ratio under the T3 treatment was higher than the other treatments at each growth stage(except for the maturity stage),while the root-shoot ratio under the T4 treatment was lower than the other treatments.The stem sheath and leaf dry weight under the T1 and T2 treatments were significantly higher than the T3 and T4 treatments,with no significant difference between the T1 and T2 treatments.The spike dry weight under the T2 and T3 treatments was significantly higher than the other treatments,while the T4 treatment was significantly lower than the other treatments,and there was no significant difference between the T2 and T3 treatments.The aboveground dry weight of Longdao 18 was consistently higher than Dongnong 427 under each treatment.(6)Under the T1,T2,and T3 treatments,the number of effective panicles per unit area was significantly higher than the T4 treatment,while the 1000-grain weight was significantly lower than the T4 treatment,and there was no significant difference in the number of grains per panicle and the grain filling rate among the treatments.The actual yield of both varieties showed the following trend: T2 > T3 > T1 > T4,with no significant difference between the T1,T2,and T3 treatments,but all of them were significantly higher than the T4 treatment.The water use efficiency showed the following trend: T4 > T2 > T3 > T1,with the T4 treatment significantly higher than the other treatments,the T1 treatment significantly lower than the other treatments,and no significant difference between the T2 and T3 treatments.In summary,the alternate wetting and drying irrigation during the critical tillering leaf age(T2 treatment)can enhance nitrogen accumulation,key enzyme activities of nitrogen metabolism in functional leaves and grains,sap flow intensity,amino acid content in sap,protein content and composition in grains,and spike dry weight of both varieties compared to the other treatments.It also shows higher water use efficiency and the highest actual yield.Therefore,under the experimental conditions,the alternate wetting and drying irrigation during the critical tillering leaf age is considered the preferred irrigation method. |
