Effect Of Drought Stress At Tillering Stage On Root Growth And Nitrogen Metabolism Of Japonica Rice In Cold Region

Rice is the main food crop,and drought has a great impact on rice.The tillering stage is one of the stages that are relatively sensitive to drought.The drought stress at the tillering stage affects the number of effective panicles of rice,which in turn affects the yield of rice.The root system is the organ that absorbs water and nutrients in rice,and it is closely related to the growth and development of the above-ground organs and yield quality.Nitrogen metabolism is an important nutrient metabolism pathway of rice.Drought stress severely affects the activity of nitrogen metabolism enzymes and then affects the growth and development of rice.In this experiment,Songjing 6 and Dongnong 425 were selected as rice varieties,and normal irrigation was us ed as control,three drought gradients of mild drought(-10KPA),moderate drought(-25kpa)and severe drought(-40kpa)were set to explore the effects of different degrees of drought stress on root morphology,nitrogen metabolism system and yield components of rice at the tillering stage,in order to clarify the response of root characteristics and nitrogen metabolism under different degrees of drought stress,reveal the internal mechanism of nitrogen metabolism and root growth and development on yield formation of rice under drought stress at tillering stage,so as to provide technical support and theoretical basis for agricultural production to provide drought tolerant rice varieties and explain the physiological mechanism of drought resistance of rice.The results are as follows:(1)Mild drought stress during the tillering stage and after rewatering promoted the growth of total root length,root volume,root surface area and average root diameter,while moderate and severe levels inhibited growth,and severe drought had a greater impact on rice root morphology.There were also differences between the two cultivars under the same treatment.The increase in the total length,root volume,and root surface area of Songjing 6 during the tillering stage and after the rewatering under mild drought treatment was less than that of Dongnong 425.The reduction of total root length,root volume and root surface area of Songjing 6 under moderate and severe drought treatments were higher than that of Dongnong 425.(2)During the tillering stage and after rewatering,the root activity of the mild drought treatment was not significantly different from the control treatment.The moderate and severe drought treatments were significantly lower than the control treatment,an d the moderate drought treatment decreased less than the severe drought.Correlation analysis showed that root activity was closely related to yield.(3)The content of soluble protein and proline in roots of Japonica rice increased during the tillering stage and after rewatering.There are differences between the two cultivars.The soluble protein and proline content of the root system of Songjing 6 increased lower than that of Dongnong425 under moderate and severe drought.(4)The activities of nitrogen metabolism enzymes(except GDH)in roots of Japonica rice increased under mild drought treatment during the tillering stage and after rewatering,but decreased under moderate and severe drought treatment,and the more severe the drought was,the greater the decline was.The GDH activity increased with the decrease of soil water potential.There were also differences between the two varieties under the same treatment.during the tillering stage and after rewatering,the activity of nitrogen metabolism enzyme s in the roots of Dongnong 425 under mild drought treatment was higher than that of Songjing 6,and the activity of nitrogen metabolism enzymes in the roots of Songjing 6 under moderate and severe drought treatment was higher than that of Dongnong 425.(5)Nitrogen accumulation in the shoots and roots of japonica rice,and the proportion of nitrogen accumulation in the shoots in cold regions decreased during each growth stage.And the decline was severe> moderate> mild.There were also differences between t he two varieties under the same treatment.The above-ground and root nitrogen accumulation of Dongnong 425 under mild drought treatment were not significantly different from those of the control treatment.The decrease of nitrogen accumulation in shoot,root and proportion of nitrogen accumulation in shoot in T2 and T3 treatments of Songjing 6 was greater than that of Dongnong 425.(6)The dry weight of shoot and root decreased with the decrease of soil water potential at each growth stage.The root shoot ratio of mild drought treatment was higher than that of the control treatment,while that of moderate and severe drought treatment was lower than that of the control treatment.Compared with the control treatment,the increase of root shoot ratio of Dongnong 425 under mild drought treatment was higher than that of Songjing 6,and the decrease of root shoot ratio under moderate and severe drought treatment was lower than that of Songjing 6.(7)After drought stress at tillering stage,the yield of Japonica Ri ce in cold region decreased in all treatments,and the decline range was severe > moderate > mild.There were also differences between the two varieties under the same treatment,and the decline range of Songjing 6 was higher than that of Dongnong 425.Correlation analysis showed that there was a significant positive correlation between root indexes and yield under drought stress at tillering stage.There was a significant positive correlation between root enzyme activity(except GDH)and yield.It shows that the decline of yield is closely related to the above indexes.