| This study was based on the theory of ecological stoichiometry and took the Broussonetia papyrifera which was the suitable tree of the comprehensive control demonstration area of rocky desertification ecological construction in Guanling Zhenfeng Huajiang as the research object.The content of tissue(leaves,branches,fine roots)of B.papyrifera-litter-rhizosphere soil continuum organic carbon(C),total nitrogen(N),total phosphorus(P),total calcium(Ca),total magnesium(Mg)and C,N,P stoichiometric characteristics,and their correlation with different rocky desertification degrees were analysis.Moreover,the interaction of B.papyrifera-litter-rhizosphere soil continuum was discussed,and combined with redundancy analysis(RDA)to explore the coupling relationship between the stoichiometric characteristics of B.papyrifera-litter-rhizosphere soil continuum and environmental factors.The purpose of this paper was to further understand the plant nutrient cycling law and system stability mechanism of the fragile karst rocky desertification ecosystem in Southwestern China,and to provide scientific theoretical basis for the vegetation reconstruction and ecological restoration of different degrees of rocky desertification environment.The main results were as follows:(1)The results of the study on the general characteristics of chemometrics of the B.papyrifer-litter-rhizosphere soil in karst rocky desertification environment showed that: the organization of B.papyrifera had obvious characteristics of low P and high Ca,and its growth was mainly restricted by P.In terms of the variation of nutrient content,the variation degree of Ca and Mg in the B.papyrifer-litter-rhizosphere soil continuum was greater than C,N and P.Moreover,in terms of nutrient content distribution,the leaf nutrient content was the highest in all tissues of the B.papyrifer,and the C content in different tissues of B.papyrifer and the litter was significantly higher than that in the rhizosphere soil,while the content of P,Ca and Mg in fine root were lower.The correlation analysis showed that there was a strong correlation between litter N,P content and the ratios of other nutrient elements in leaf,branch,fine root and litter.There was a significantly negative correlation between leaves,branches,and fine roots N content and their C:N(P<0.05),and the content of Ca and Mg was negatively correlated in fine roots(P<0.05).The results of correlation analysis showed that Among them,the correlation coefficient between litter P content and litter N:P was the largest,and the correlation between Litter C:N and other nutrient content and ratios in litter was not significant.In addition,the correlation coefficients of N content and C content,N content and P content,and C:P and C:N in rhizosphere soil were all significantly positively correlated(P<0.05).(2)The results of the study showed that the B.papyrifera-litter-rhizosphere soil continuum as a whole had a good coupling relationship.The content of nutrients in different tissues of B.papyrifera was significantly positively correlated(P<0.05),among which fine root was the most significantly correlated with leaf.The content of P,Ca,Mg and C:P,N:P were positively correlated with the corresponding content and stoichiometric ratio of litter(P<0.05),but the correlation between branches and the stoichiometric characteristics of litter was not significant.Except that the content of fine root N was negatively correlated with the rhizosphere soil N,there was significant correlation between the stoichiometric characteristics of different tissues of B.papyrifera and rhizosphere soil nutrients(P<0.05),and the correlation coefficient between the stoichiometric characteristics of fine roots and rhizosphere soil was greater than that of leaves and branches;there was significant positive correlation between the nutrient content of litter and rhizosphere soil(P<0.05),while the C,N,P ratios of litter and rhizosphere soil was significant negative correlation(litter N:P and rhizosphere soil C:P,N:P)or not Close(litter C:N,C:P and rhizosphere soil C:N,C:P).(3)The response of stoichiometric characteristics of B.papyrifera-litter-rhizosphere soil continuum to the succession of rocky desertification was different,but it had its similarity.In terms of nutrient content distribution,the content of N and P in B.papyrifera leaves were significantly lower in potential rocky desertification environment,and the content of Ca and Mg were significantly higher in intensity rocky desertification environment.The contents of N and P in fine roots were lower in Nil rocky desertification environment,and the contents of Mg increased with the increase of rocky desertification degree.The contents of C and N in litter were significantly higher in Nil rocky desertification environment,and the content of Ca and Mg was the highest in the intensive rocky desertification environment.The content of N,P and Mg inrhizosphere soil was lower than that in the moderate and intensive rocky desertification environment,and the nutrient of rhizosphere soil fluctuates obviously,especially the content of Ca increases with the increase of rocky desertification degree.The ratio of C,N and P were as follows: the change trend of C:P in different degrees of rocky desertification environment was very different.The overall change rule of C:N in different tissues of B.papyrifera and rhizosphere soil was basically the same,both of which were decreased first and then increased.Moreover,the change tend of N:P in different degrees of rocky desertification environment was similar to that in rhizosphere soil,that was,increased first,then decreased and then increased.In addition,the regression analysis between the stoichiometric characteristics of the B.papyrifera-litter-rhizosphere soil continuum and the rocky desertification level showed that there was no functional relationship between the rocky desertification level and the C content of leaves,C content of branches,P content of branches,Ca content of fine roots,Mg content of branches,P content of rhizosphere soil,Mg content of rhizosphere soil,C:P of branches,N:P of fine roots,C:N of Rhizosphere Soil and litter,N:P of rhizosphere soil.The results show that there was a quadratic function relationship between nutrient content and stoichiometric ratio of other components and rocky desertification level,and a few of them were linear correlation,which reflects the linear and nonlinear coupling characteristics between the chemical stoichiometric characteristics of B.papyrifera-litter-rhizosphere soil continuum and rocky desertification level.(4)Based on the environmental factors such as human activity inten-sity,rocky exposedness rate,vegetation coverage,altitude,slope and aspect,RDA was used to analyze the degree of influence on the stoichiometric characteristics of B.papyrifera-litter-rhizosphere soil continuum.The rocky exposedness rate,vegetation coverage,and human activity intensity have the greatest impact on the stoichiometric characteristics of B.papyrifera,the degree of interpretation was44.23%,44.05%,and 36.11%,respectively.The environmental factors that had the greatest impact on the stoichiometric characteristics of litter were the intensity of human activities,the rate of rock exposure and vegetation coverage,with the interpretation degree of 47.84%,45.97% and39.96% respectively.However,the rocky exposedness rate,altitude,and human activity intensity had the greatest impact on the stoichiometric characteristics of rhizosphere soil,and the degree ofexplanation was respectively 45.59%,16.32% and 16.32%.It can be seen that the rocky exposedness rate and the intensity of human activities were the two most critical environmental factors that affect the changes of the stoichiometric characteristics of B.papyrifera-litter-rhizosphere soil continuum. |
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