Effects Of Intercropping Pasture On The Growth And Physiological Characteristics Of Olive Root System Under Drought Stress

Olive(Olea europaea L.),with high economic value and ecological benefits,is a world-famous high-quality woody oil and fruit tree,the coast of the Bailong River in Gansu province is one of the three most suitable habitats for olive production in China.However,olive of Longnan is planted in many mountainous areas with poor irrigation conditions,which affects the growth and development of olive.The problem of drought and water shortage has become one of important factors restricting the local olive production.Intercropping pasture has many advantages,such as improving soil fertility,reducing soil and water loss,adjusting the microclimate of the orchard,and reducing the harm of orchard pests and diseases,etc.Pot-culture experiment method was adopted in this study.The experimental water-control settings were normal watering(the soils water content were 18%(CKw)),mild drought(the soils water content were 15%),moderate drought(the soils water content were 12%),and severe drought stress(the soils water content were 9%);Under different water conditions,3 intercropping treatments were set up within the pots of olive seedlings: intercropping alfalfa,intercropping red clover,intercropping alfalfa+red clover with non-intercropping as control.Under different pasture intercropping and drought stress conditions,the root morphological index,physiological index,rhizosphere soil organic matter content,and soil enzyme activity of olive were measured and correlated,and the drought resistance of different intercropping was compared by using the method of subordinate function analysis,to reveal the effects of intercropping pasture on olive roots under drought stress,in order to provide technical guidance and theoretical support for improving drought resistance production of olive.The main results are as follows:(1)Light water stress promoted to the increase of total root length and root biomass,and drought stress was intensified,the total root length,root average diameter,total surface area and total root volume of olive root system significantly reduced,while the reduction rate was slowed down by intercropping pasture.Intercropping pasture could significantly increased root biomass,specific root length and specific root area of olive compared with non-intercropping.Red clover intercropping was the most significant treatment.With the decreased of soil water content,the root tissue density of olive increased,and the intercropping alfalfa and alfalfa + red clover were higher than non-intercropping under severe drought stress.(2)With the decrease of soil water content,the root activity and relative water content of olive root decreased significantly,and the reduction rate was slowed down by intercropping pasture.As the stress of drought was intensified,the olive root relative conductivity and malondialdehyde content(MDA)gradually increased,the olive root was subjected to oxidative stress caused by drought,while intercropping red clover and intercropping alfalfa significantly inhibited relative conductivity and MDA.The contents of proline(Pro),soluble sugar(SS),the activity of peroxidase(POD)and catalase(CAT)of olive root increased significantly by intercropping pasture,while the superoxide dismutase(SOD)did not significantly increase.(3)The content of organic matter in rhizosphere soil of olive decreased with the aggravation of drought stress,and the largest decrease was in severe drought(54.73%).The soil organic matter content was slowed down after intercropping pasture,and reached the maximum under mild drought stress,and the intercropping red clover had the best effect(65.56%).Soil urease activity and alkaline phosphatase activity in non-intercropping were only higher than that in intercropping pasture under mild drought stress.Under severe drought stress,alkaline phosphatase activity in alfalfa + red clover had no significant difference with that in non-intercropping(P<0.05),while that in other non-intercropping increased significantly.Under drought stress,soil invertase activity was higher than that in non-intercropping after intercropping pasture,and there was no significant difference in soil catalase activity between intercropping alfalfa and intercropping red clover except mild drought(P<0.05),and the effect was significantly improved under other drought stress.(4)The correlation analysis and subordinate function analysis showed that intercropping pasture could significantly enhance the drought resistance of the roots of potted olive seedlings,while intercropping red clover treatment had stronger.