Responses Of C,N,P Stoichiometric Characteristics Of Plant Communities And Litters To The Evolution Of Rocky Desertification In Karst Ecosystem

Based on the theory of ecological stoichiometry and using the method of space instead of time,different degrees of rocky desertification in karst plateau canyon of Guanling-Zhenfeng Huajiang in Guizhou Province was studied.Firstly,five rocky desertification degrees were selected as our research object,that is,nil,potential,slight,moderate and high.Then,the C,N,P ecological stoichiometric characteristics and N,P nutrients absorption rates of four plant layers(trees,shrubs,herbs,dominant species)and litter layer in different degrees of rocky desertification were analyzed.We also studied the relationships between the C,N,P ecological stoichiometric characteristics of each component and its response to the succession of karst rocky desertification.Finally,combined with redundancy analysis(RDA),the coupling relationship between the C,N,P ecological stoichiometric characteristics and environmental factors of plant communities and their litter was discussed.Through these studies,we hope to further understand the plant nutrient cycling and system stability mechanism of fragile karst rocky desertification ecosystem in Southwest China,and provide scientific theoretical basis for vegetation rehabilitation and ecological restoration in different degrees of rocky desertification.The main results are as follows:(1)The general characteristics of C,N,P ecological stoichiometry of plant communities and litters.The results showed that plants communities and their litters have high C and P contents and low N contents,indicating that the C,N,P contents of litter have similar characteristics to plants,reflecting that the litter has characteristics of adhering to plant characteristics.In the study area,the leaf C:N was higher in the plant communities,but the N:P(the average value was 6.52)was very low,indicating that the plant growth in the study area was limited by the N nutrients.The correlation analysis results showed that the N contents of plants communities and their litter were significantly and positively correlated with the contents of C and P(P<0.01),while C:N and C,N contents,C:P and P content,N:P and N,P contents were a significant and negative correlation(P<0.05).The characteristics of N and P nutrient absorption rates in the plant communities and their litter show that the spatial variability of N nutrient absorption rate in the rocky desertification environment is smaller than that of P nutrient.(2)Ecological stoichiometric characteristics of C,N,P at different levels of plant commutities and litters.Arbor leaves had the highest contents of C,C:N,C:P and N:P,and the lowest N and P contents.The N content of shrub leaves was the highest,their C:N was the smallest.The C,C:P and N:P of herbaceous leaves were lower than those of other plant communities,but had the highest content of P.Correlation analysis showed that the content of N was significantly and negatively correlated with C:N(P<0.05)of each layer of plant communities and their litter,and the content of P was significantly and negatively correlated with C:P and N:P(P<0.05),while C:P and N:P were significantly and positively correlated(P<0.05).Among the various layers of plant communities and their litter C,N,P contents and their stoichiometric characteristics existed significant and positive correlation(P<0.05)between shrub and herb.(3)Responses of C,N,P stoichiometric characteristics at different levels of plant communities and litters to the evolution of rocky desertification With the increased degree of rocky desertification,the contents of N and P in each layer of plants and litter showed a trend of increasing first,then decreasing and increasing last,while C:N,C:P and N:P showed the opposite trend with N and P content,showing decreasing first,then increasing and increasing last.There was no significant difference in the absorption rate of N and P nutrients between plant communities and their litter systems in different degrees rocky desertification(P>0.05).With the increased degree of rocky desertification,the rate of N nutrient absorption showed a trend of decreasing first and then increasing,while the rate of absorption of P nutrient showed the opposite trend of N nutrient absorption rate,which increased first and then decreased.(4)The RDA analysis for environmental factors associated with C,N,P ecological stoichiometry of plant communities and litters.The RDA analysis shows that human activity intensity,altitude and community coverage are the three major environmental factors that drive the changes of C,N,P ecological stoichiometric characteristics in plant communities and litters in karst rocky desertification environment.The intensity of human activities mainly affects the contents of N,P in plant comunities and the contents of C,N,P in litter,while altitude mainly affects and the contents of C,N in plant comunities and the content of C,C: N,C: P in litter.Vegetation coverage has a certain influence on the content of C,N,P and stoichiometric characteristics of plant communities and litters,but the influence is relatively slight.