Effects Of Nitrogen Addition On Fine Root Traits And Rhizosphere Soil Nutrient Characteristics Of Typical Plant Seedlings Under Karst Rocky Desertification Control

Fine root(?2mm)is the most active and sensitive part of root tissue,which is a key organ for plant to absorb water and nutrients.This study on karst rocky desertification governance typical plant of Zanthoxylum bungeanum and Medicago sativa seedlings as the research object,We performed pot control experiment,there were four treatments:blank control(CK),low nitrogen(LN),medium nitrogen(MN)and high nitrogen(HN),respectively study Zanthoxylum bungeanum and Medicago sativa seedlings fine root biomass,fine root morphology,and fine root chemistry traits and rhizosphere soil nutrient characteristics response to nitrogen addition,and analyzes the mutual coupling between them,To explore the change mechanism of fine root adaptation strategies of the two plants under the influence of nitrogen addition and the interaction mechanism with rhizosphere soil nutrients,in order to provide important physiological and ecological theoretical basis for vegetation ecological restoration and management in rocky desertification areas under the background of future climate change.The main research results are as follows:(1)Nitrogen addition promoted the increase of fine root biomass of Z.bungeanum and M.sativa seedlings,and both reached the medium under in treatment.With the increase of N concentration,the fine root biomass of Z.bungeanum decreased,while that of M.sativa increased first,then decreased,and then increased.In addition,the fine root morphology of Z.bungeanum and M.sativa seedlings had no significantly change except that the specific root length and specific surface area of 0-0.5mm diameter class of M.sativa were significantly affected by N addition.The results of two-way ANOVA indicated that fine root diameter significantly affected the average diameter,specific root length,specific surface area and tissue density of Z.bungeanum and M.sativa,while nitrogen addition had no significant effect on the fine root morphological traits of Z.bungeanum and M.sativa seedings.(2)With the increase of N concentration,the N content of fine roots of Z.bungeanum and M.sativa seedlings increased,the content of C and P decreased,the content of C:P and N:P increased,and the content of Mg and Ca had no significant change.N was still the nutrient element limiting the growth of M.sativa seedlings,and the growth of Z.bungeanum seedlings was easily limited by N and P.The results of two-way ANOVA indicated that the fine root diameter had an significant effect on the content of C,N,P and C:N,C:P,N:P in the fine roots of Z.bungeanum and M.sativa seedlings.With the increase of fine root diameter,the content of N and P in the fine roots of Z.bungeanum and M.sativa significantly decreased,while the content of Mg and Ca remained stable.Nitrogen addition not only significantly affected N content,C:P,N:P of fine root of Z.bungeanum seedlings,but also significantly affected C,N,P content and C:N,C:P,N:P of fine root of M.sativa seedlings.(3)Through the correlation analysis of the stoichiometric characteristics of the nutrient elements in fine roots of Z.bungeanum and M.sativa seedlings,it was found that the C,N,P and Mg element contents of the fine roots were mostly positively correlated,while the contents of Ca were mostly negatively correlated,and the correlation of C,N and P in fine roots of each diameter class was greater than that of Mg and Ca.In addition,the correlation analysis between morphological characteristics of fine roots and nutrient elements of fine roots of Z.bungeanum and M.sativa seedlings showed that the specific root length and specific surface area of 0-0.5mm diameter class were positively correlated with the content of C,N,P,ect of fine roots,while those of1-2mm diameter class were negatively correlated,which may be related to the function of different grades of fine roots in the root system.(4)Nitrogen addition significantly increased the contents of TN,NO₃^--N and NH₄⁺-N in fine rhizosphere soil of Z.bungeanum and M.sativa seedlings,but significantly decreased the SOC content of M.sativa rhizosphere soil,but had no significant effect on the contents of TP,Mg,Ca and p H value in rhizosphere soil of the two plants,leading to the decrease in the C:N value of the rhizosphere soil and a significant increase in the N:P value.In addition,the results of the correlation analysis of rhizosphere soil nutrients of fine roots of Z.bungeanum and M.sativa seedlings showed that the contents of SOC and TN in rhizosphere soil were highly coupling,and they were significantly positively correlated with TP,Mg,NO₃^--N,NH₄⁺-N,ect(P<0.05),while the correlation between TP and other nutrient elements in rhizosphere soil was low,and the effect of nitrogen addition on TP content in rhizosphere soil of two plants was not obvious.(5)Redundancy analysis(RDA)results showed that there was a close correlation between rhizosphere soil nutrients and fine root morphology and chemical characteristics,which showed that fine roots of Z.bungeanum and M.sativa mainly change the specific root length and the specific surface area to changes in the soil nutrient environment caused by nitrogen addition,while average diameter and tissue density had a weak response to nitrogen addition.In addition.Most of the nutrient elements in fine roots of Z.bungeanum and M.sativa were positively correlated with the corresponding nutrients in rhizosphere soil,while most of them were negatively correlated with Ca in rhizosphere soil.The results showed that Ca had little effect on it,while C,N and P were still the main nutrient factors effect the growth of fine roots of seedings.