Regulatory Effects Of Exogenous Glucose On Apple Rooting Zone Carbon Turnover,Root Architecture And Nitrogen Metabolism

The dominant apple producing areas in China are mostly built in hilly and mountainous areas with lower soil organic matter（SOM）.The mineralization of SOM is aggravated by clear tillage system and the insufficient input of organic fertilizer.The long-time less input than output and decreasing quality of soil carbon seriously restrict the orchard productivity.Exogenous carbon supplement is the basic way to solve the above problems.Increasing soil quality and improving the nutrient status of soil is conducive to the absorption of nutrients by roots and plant growth then realize high-quality and efficient production of apples.However,the molecular and physiological mechanisms and the relationship between the exogenous carbon and the turnover of soil carbon pool in the root zone and the root growth of fruit trees remain uncharacterized.In this research,isotope tracer technique will be used to explore the fate of target carbon after glucose supply in low carbon soil,and clarify the distribution of exogenous carbon in labile carbon pool of apple rooting zone,reveal the cascading response patterns of root topology to glucose,nitrogen metabolism and IAA synthesis,elucidate the response of root respiration to the effect of exogenous glucose on the accumulation of photosynthetic products1.The results of ¹³C glucose pulse labeling and soil sterilization showed that the addition of glucose and soil sterilization had different effects on the content of activated carbon pool components.The content of labile carbon pool components in soil added with 500%microbial biomass carbon（MBC）was higher than that added with 100%MBC.The components of labile carbon pool added with 500%MBC in sterilized and non sterilized soil increased,on average,by 48.4%and 35.3%compared with the control（adding distilled water）.The contents of SOC,MBC and WSOC all peaked at 7 days,and then decreased slowly.During the whole sampling period,the residual rate of glucose carbon decreased gradually,and the residual rate of sterilized soil with the same level of glucose addition was higher than that of non sterilized soil.No matter whether the soil was sterilized or not,exogenous glucose added increased the richness index and diversity index of soil bacterial community compared with the control.The composition of bacterial community in sterilized and non sterilized soil was similar,but the relative abundance of Proteobacteria,Actinobacteria,Firmicutes and Bacteroidetes increased significantly in sterilized soil.The addition of glucose optimized the nutrient conditions in the root zone and improved the root activity,morphological structure and biomass.The addition of high level glucose increased the content of NO₃^--N and NO₂^--N in roots,decreased the content of NH₄⁺-N,increased the activity of key enzymes of nitrogen metabolism and their gene expression,and promoted the assimilation of nitrogen and the transformation to amino acids in roots.2.The experiment of adding glucose(3 g·kg^-1,about 500%MBC glucose)to the root zone of’Hanfu’apple and soil sterilization showed that the root activity of exogenous glucose（Glu）and sterilized soil glucose（SS+Glu）was 44.1%and 36.8%higher than that of the control（distilled water）respectively,and the peak appeared 15 days after treatment.Glu and SS+Glu increased the content of different forms of nitrogen in roots.Glu increased the contents of NO₃^--N and NO₂^--N in roots by 33.1%and 30.1%,and significantly increased the activities of Nitrogen Metabolism Assimilation Enzyme and transaminase in roots.In addition,under Glu treatment,the plant height,total biomass and root biomass of’Hanfu’apple increased significantly by 19.7%,17.7%and 26.6%respectively.Therefore,500%MBC glucose can improve root activity and nitrogen metabolism in low-carbon sandy soil,which is conducive to the increase of plant height and the accumulation of dry matter.3.The results of integration of root architecture,root nitrogen metabolism,and photosynthesis to reveal the cross-talk between glucose and IAA in‘Hanfu’apple trees showed that altering to m RNA levels of various genes related to root growth,auxin transport and biosynthesis.G,I and G+I significantly increased the expression of lateral root development genes（SHY2,LBD11 and ALF4）,auxin synthesis（TAA1,YUCCA8 and TAR2）and transport（PIN1,LAX2 and AUX1）,increased the content of endogenous auxin in roots,improved root architecture,increased branching structure,and made roots tend to two branching type.At the same time,G,I and G+I accelerated the root nitrogen metabolism cycle,increased the activity of key enzymes of nitrogen metabolism and gene expression,and increased the transformation of inorganic nitrogen into organic nitrogen,which was conducive to the improvement of photosynthetic performance and biomass accumulation.However,T increased the expression of auxin synthesis genes,but decreased the expression of transport related genes,damaged the auxin cycle,decreased the endogenous content of roots,and reduced the process of root growth and development and nitrogen metabolism.Compared with T,G+T increased auxin content by increasing auxin synthesis and transport gene expression,and effectively slowed down the adverse growth of roots caused by Tiba.In addition,exogenous addition of glucose（G,G+I and G+T）can also improve the nutrient content of root zone and increase microbial activity.The above shows that glucose and/or indoleacetic acid promote the absorption capacity of roots to nitrogen,improve the conversion of more inorganic nitrogen into organic nitrogen and produce more organic matter for leaf photosynthesis,and then increase the biomass of plants.The combination of glucose and indoleacetic acid is the best.4.Foliar fertilizer spraying is an important agronomic measure in production,which is used to alleviate the lack of soil nutrients and hinder the absorption of nutrients by roots.The experiment of foliar spraying glucose on’Hanfu’apple in low-carbon soil showed that continuous spraying of glucose(10 mmol·L^-1)for 5 days during the rapid growth period significantly increased stomatal opening,intercellular carbon dioxide concentration（Ci）,net photosynthetic rate（Pn）and stomatal conductance（Gs）,and increased the maximum photochemical efficiency（F_v/F_m）.At the same time,carotenoid content and chlorophyll a/b value also increased.In addition,after spraying glucose,the antioxidant system of leaves was enhanced,the content of total soluble sugar and the activities of key enzymes of sucrose metabolism were increased,the activities of glutamine synthase（GS）and 1,5-ribulose bisphosphate carboxylase（Rubisco）in carbon and nitrogen metabolism were increased,more photosynthetic carbon was produced and transported underground,which provided energy and substrate for root respiration,and then increased the rate and activity of root respiration,It is beneficial to the change of root nitrogen cycle and morphological structure...