Fine Root Architecture Of Typical Adaptive Plants And Its Correlation With Stoichiometric Characteristics Of C,N,P Nutriments In The Karst Rocky Desertification Ecosystem

This study was based on the root architecture and the theory of ecological stoichiometry,and took the Broussonetia papyrifera,Zanthoxylum bungeanum,Ribes burejense and Pyracantha fortuneana which were the adaptive plants of comprehensive control demonstration area of karst rocky desertification ecological construction in Guanling-Zhenfeng huajiang as the research objects.The fine root architecture(topology,total root length,branching rate,ratio of cross-section areas)of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana in karst ecosystem,and the ecological stoichiometric characteristics of total organic carbon(C),total nitrogen(N)and total phosphorus(P)in fine-root rhizosphere soil and the adaptive strategies to karst rocky desertification were analysis.The correlation between fine root architecture and fine-root rhizosphere soil nutrients was discussed,and combined with principal component analysis(PCA)to explore the main factors affecting of fine root architecture.The purpose of this paper was to further understand the fine root branching strategy of adaptive plants in Karst Rocky Desertification in Southwest China and the influence mechanism of nutrients on fine roots,and to provide scientific theoretical basis for promoting the ecological restoration and management of karst rocky desertification environment and the selection of ecological tree species.The main results were as follows:(1)The fine root topological indexes of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were TI=0.93,TI=0.95,TI=0.95 and TI=0.94 respectively,which were typical Herringbone branching patterns with high topological indexes.The fine root connection length was longer,and the total root length and average root length were more than 800mm and 9mm,respectively.The total root length was B.papyrifera>R.roxburghii>P.fortuneana>Z.bungeanum and the average root length was R.roxburghii>B.papyrifera>Z.bungeanum>P.fortuneana.The branching rate of fine root was smaller and the ratio of cross-section areas of the B.papyrifera and R.burejense before and after fine root branching were no significant difference and 1.04 and 1.03 respectively,which were consistent with Leonardo da Vinci's law.The fine root morphology of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana had obvious plasticity and different morphological characteristics,among which the fine roots of B.papyrifera,R.roxburghii and P.fortuneana were herringbone system.The correlation of fine root architecture parameters was as follows:Z.bungeanum>R.roxburghii>P.fortuneana>B.papyrifera,and the correlation coefficients of topological depth A,average topological depth b,Total links from all bases to terminals Pe,Number of total exterior links M,and topological index qa,qb,TI were all high,and showed extremely significant positive correlation(P<0.01).(2)The nutrient contents of fine roots and rhizosphere soil of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were lower than those of other plants in karst rocky desertification.The C and N contents of fine roots were higher than those of rhizosphere soil,and the P content of fine roots was lower than that of rhizosphere soil.The correlation analysis of fine root nutrients showed that B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana showed a consistent rule,that is,the content of N and P significantly affected the content and stoichiometry of other nutrient elements.The C:P and C content of Z.bungeanum and R.roxburghii were significantly positively correlated(P<0.05),the C:P and N content of Z.bungeanum were significantly positively correlated(P<0.05),the P content of B.papyrifera and P.fortuneana were significantly positively correlated(P<0.05),the<C:N and N contents of Z.bungeanum,R.roxburghii and P.fortuneana were significantly negatively correlated(P<0.01),N:P and N contents of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were significantly positively correlated(P<0.01),C:P and N:P contents of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were significantly negatively correlated(P<0.01),and N and P contents of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were significantly negatively The most critical nutrient element for growth.The correlation results of rhizosphere soil nutrients showed that there was a strong correlation between the rhizosphere soil nutrient content and the stoichiometric ratio,among which the N content,C:N,C:P and C content of Z.bungeanum and P.fortuneana were highly significantly positively correlated(P<0.01),while the P content and C content of Z.bungeanum and P.fortuneana were highly significantly positively correlated(P<0.05),and the C:P,N:P and P content of B.papyrifera,Z.bungeanum,R.roxburghii and P.fortuneana were significantly positively correlated(P<0.05).The C:N,C:P and P content of B.papyrifera were negatively correlated(P<0.05),the C:P and P content of R.roxburghii were negatively correlated(P<0.05),and the N:P and N:P of B.papyrifera,Z.bungeanum,and P.fortuneana were positively correlated(P<0.01).(3)The correlation between fine root architecture and fine root nutrients of B.papyrifera,Z.bungeanum,R.roxburghii,P.fortuneana in karst rocky desertification showed that there was a significant negative correlation between fine root P content of B.papyrifera and total fine root length(P<0.05),a significant positive correlation between fine root n:P content of Z.bungeanum and total fine root branching rate(P<0.05),and a significant negative correlation between fine root P content of R.roxburghii and topological index qa,TI.There was a significant positive correlation between C:P and topological index qa,qb,TI(P<0.05),and a significant negative correlation of P.fortuneana between N content and total root length(P<0.05).There was no significant correlation between other indexes of four kinds of adaptive plants(P>0.05).The results of correlation between fine root architecture and rhizosphere soil nutrients showed that C content in rhizosphere soil of B.papyrifera was significantly positively correlated with the percentage of total score(P<0.01),C content and C:N in rhizosphere soil were significantly negatively correlated with the ratio of cross-sectional area before and after fine root branching(P<0.05),C content and C:N in rhizosphere soil of Z.bungeanum were significantly positively correlated with fine root topological index qa,qb,TI(P<0.05),and C:N in rhizosphere soil was significantly positively correlated with fine root topological index qa,qb,TI(P<0.05).The content of C,N,C:P in rhizosphere soil was positively correlated with the cross-sectional area of fine roots(P<0.05),and the content of C:P in rhizosphere soil was negatively correlated with the total branching rate of fine roots(P<0.05).There was a significant negative correlation of R.roxburghii between C content in rhizosphere soil and total branching rate of fine roots(P<0.01),a significant negative correlation between P content in rhizosphere soil and total branching rate of fine roots(P<0.05),and a significant positive correlation between C:P content in rhizosphere soil and total length of fine roots(P<0.05).It could be seen that the C content in rhizosphere soil is the key factor of root branching strategy,and the correlation between rhizosphere soil nutrients and fine root configuration is stronger than that between fine root nutrients and fine root configuration,which may be related to the fact that rhizosphere soil is the most important and direct source of fine root nutrients,and the function of fine root is to absorb water and nutrients in rhizosphere soil.(4)principal component analysis(PCA)based on fine root architecture parameters of B.papyrifera,Z.bungeanum,R.roxburghii,P.fortuneana showed that the contribution rates of principal components 1,2,3,4 and 5 were 26.708%,24.897%,11.922%,8.779%and 8.392%respectively,which could explain 80.066%of the original 17 variables.In principal component 1,it was highly correlated with topological length a,average topological length B,total branching rate and stepwise branching rate R₄/R₅;in principal component 2,it was highly correlated with topological index qa,qb and TI;in principal component 3,it was highly correlated with total root length and average longer height;in principal component 4,it was highly correlated with cross-sectional area ratio.It could be seen that fine root topological index,total root length,average root length,total branching rate,gradual branching rate and cross-sectional area ratio were important parameters of fine root architecture.Principal component analysis(PCA)of fine root architecture based on nutrient characteristics showed that the contribution rates of principal components 1,2,3 and 4 were 32.129%,29.739%,16.233%and 11.974%respectively,which could explain 90.076%of the original13 variables.Principal components 1,2,3 and 4 were mainly related to fine root rhizosphere soil nutrient and stoichiometric ratio,and species height,indicating that they were the main factors affecting fine root architecture.