Effect Of Nitrogen Level On The Root Morphology And Physiological In Catalpa Bungei Under Local Drought

Catalpa bungei is an important native tree species in China with strong adaptability and wide distribution.Catalpa bungei has the advantages of straight and perfect tree shape,fine and dense wood,which is an important precious timber species in northern China.Because Catalpa bungei is mainly distributed in semi-arid and semi-humid areas in China,and its growth speed is fast and nitrogen demand is large,drought and lack of nitrogen nutrition are two important factors that restricting the productivity of Catalpa bungei plantation.The research on water utilization efficiency and nitrogen utilization efficiency of Catalpa bungei is an effective way to deal with drought stress and nitrogen deficiency,and to improve the productivity of Catalpa bungei plantation.Compared with agricultural cultivated soil,forest soil usually has local root-zone droughts in both horizontal and vertical direction.It is of great theoretical significance and practical application to deeply study the physiological response and nitrogen regulation of Catalpa bungei roots to local soil drought in horizontal and vertical directions,and reveal the characteristics of drought signal response and water use efficiency under local drought.Under this background,the effects of local drought,nitrogen nutrition and their coupling on morphological development and physiological response of Catalpa bungei roots were studied.The main conclusions are as follows:(1)The root development and root architecture of Catalpa bungei have self-regulation and adaptation mechanisms to different types of drought environment.Nitrogen application can enhance the root plasticity under vertical partial drought,promote the root system of Catalpa bungei to absorb deep soil water,and provide sufficient water supply for the growth and development of Catalpa bungei.Reasonable water-nitrogen interaction can promote the growth and development of Catalpa bungei roots;Compared with low nitrogen,nitrogen application could promote root growth in dry root zone and wet root zone under local drought;After nitrogen application,the roots of Catalpa bungei were more adaptable to the humid environment on the left side.The roots could fully absorb water and nitrogen,and the growth and development of roots could be coordinated through water-nitrogen interaction.(2)Nitrogen application promoted the transportation of IAA to the root tip of deep moist root zone,and promoted the root tip development and root plasticity of Catalpa bungei in moist root zone through polar transportation.In the low nitrogen environment,Catalpa bungei absorbed more water and alleviated the effect of local drought on its growth and development through the plasticity of its lateral roots;In the nitrogen supply environment,Catalpa bungei showed a significant plasticity response through the root on the wet side.Similar to the results of vertical partial drought,nitrogen application promoted the transportation of IAA to the root tip of horizontal partial drought moist root zone,promoted the root tip development of moist root zone through polar transportation,and enhanced root plasticity.(3)In the vertical partial drought environment,both the surface drought root zone and the deep moist root zone showed physiological response to drought stress,and the osmotic regulation and antioxidant defense of root increased adaptively,thus reducing the damage of surface partial drought to root system.The level of hormone induction in roots was low under local drought stress,while the accumulation of endogenous hormone in the surface and deep layers of Catalpa bungei roots was high under severe drought stress.Under the condition of low nitrogen,the content of endogenous hormones in roots of Catalpa bungei increased at both wet and dry sides;The ability of root adaptation to drought stress was enhanced by the increasing free proline and antioxidant enzymes.Different types of drought stress induced different kinds of endogenous hormones.(4)Nitrogen application could induce antioxidant enzyme activity,which appeared not only in dry lateral root zone,but also in wet lateral root zone.After nitrogen application,the kinds of endogenous hormones and antioxidant enzymes induced by different types of drought stress were different.The contents of SA,IAA,GA and JA were accumulated under complete drought stress,while IAA was induced mainly under vertical partial drought stress.SOD plays an important role in antioxidant defense under complete drought,while free proline,soluble protein and CAT are more important under vertical partial drought.Nitrogen application could induce the changes of hormone synthesis on the dry side and wet side to cope with local drought stress;Drought root zone can enhance the activity of antioxidant enzymes and induce Catalpa bungei roots to carry out antioxidant defense.Reasonable water-nitrogen interaction can improve the effect of antioxidant enzymes.This study has important guiding significance for scientific management and efficient cultivation of Catalpa bungei plantation in drought and water shortage,low nitrogen difficult site,and increase the yield and quality of Catalpa bungei wood.