| The coupling relationships between vegetation and soil have been the object of the research of ecosystem succession. The process of vegetation succession is the process of adaptation and transformation between soil and plants, and their collaborative mechanism of vegetation-soil system should have some different rules. Due to the key roles of vegetation communities, soil nutrient, soil minerals and soil microbial-communities in the process of substance circulation and energy exchanges in ecosystems, therefore, the research on the variation of four characteristics and their coupling relationships is beneficial to comprehensively understanding the rule and mechanism of ecosystem succession, which is also significant towards the recovery, reconstruction and scientific management of degraded forest ecosystem.Based on a combination of field investigation and laboratory analysis, the coupling relationship of vegetation and soil under six typical ecosystems, i.e., paddy field, dry land, grassland, Shrubbery, plantation forest, and secondary forest, in the canyon Karst region in southwest China, were analyzed. Multiple comparison analysis was used to analyze the characteristics of vegetation, soil, and soil microorganisms, and the differences between them in the six ecosystems. Cluster analysis was used to categorize ecosystems and find out the development law in succession process in the canyon karst region. Then, principal component analysis(PCA) was applied to find out the main influencing factors in the ecosystems. Lastly, canonical correlation analysis (CCA) was adopted to reveal the coupling relationships between vegetation and soil, which is of great significance to explore the coupling mechanisms during vegetation succession and ecological construction. The main results were described as follows:1. With the development of vegetation succession community, species diversity indices presented in order of herb layer> shrub layer. The maximum value of species diversity greatly appeared in the secondary forest. The carbon storage of vegetation in the six ecosystems were ordered from large to small as:artificial forest (121.53)> Secondary forest (116.76)> shrubbery (54.14)> grassland (36.05)> paddy field=dry land (0.00)103kg C-hm-2. Carbon storage of tree layer in RGL and CSL, herbaceous layer in CD and shrub layer in GC dominated the total vegetation, respectively. Besides, the carbon in the ground part was greater than in the underground part. Generally, the importance of nutrition elements was in the order of N> K>P in the overall trend.2. Soil nutrient content under the six ecosystems had a decreasing trend with soil depth except total potassium (TK). Soil fertility presented in the order of secondary forest> artificial forest> paddy field> dry land> shrubbery> grassland. In addition, soil organic carbon and soil total nitrogen content were extremely significantly and linearly related.3. The mineral nutrient of content was almost comprised of80%in the ecological system, especially SiO2, Al2O3and Fe2O3, while the proportion of other mineral nutrients was rare, relatively. The mineral nutrient decreased as an increase in soil depth, with no significant differences among the six ecosystems.4. Soil microbial populations and composition varied under different ecosystems in the canyon karst region. Soil microbial populations were largest in the secondary forest, followed by the plantation forest, while least in the dry land. Microbial composition in the six ecosystems performed in the order of bacteria> actinomycetes> fungi. Under different ecosystems, soil microbial biomass phosphorus and soil microbial biomass nitrogen, soil microbial biomass carbon were diverse, but all of them appeared to be a trend of MBC> MBN> MBP. Soil MBC and MBN was highest in the secondary forest, while MBP was highest in the plantation forest, in comparison with that MBC was lowest in the dry land, MBN and MBP were lowest in the grass. A good fractal relationship existed between soil microbial populations and soil microbial biomass at a highly significant level (p<0.01). Moreover, both soil microbial populations and soil microbial biomass in the six ecosystems decreased as an increase in soil depth.5. Soil microbial diversity was closely related to soil quality and one of research hotspots in soil science. Soil microbial functional diversity was enhanced with the increase of the training time, after reaching a certain time would be into equilibrium. The value of AWCD performed in the order of paddy field> secondary forest> grassland> artificial forest> dry land> shrubbery. Soil microbial functional diversity and community structure differed significantly between the ecosystems. Such as Shannon diversity (H), Shannon evenness (E), Simpson (D) index and richness (S) in paddy field was highest, while in the shrubbery was lowest.6. Soil aggregates were dominated by particles with size>8mm in the ecosystems except HD under dry sieving, which basically presented a trend of decreasing firstly, then increasing and finally decreasing along with particle sizes decreasing. While soil aggregates were dominated by particles with size>5mm in the ecosystems except HD under wet sieving and decreased with decreasing of particle sizes. That was to say, content of aggregate with large particle size was the highest, content of aggregate with small particle size was lowest. Soil organic carbon content was highest in the aggregate particles with0.25-0.053mm size, and the content in some particles with size>5mm was lowest. However, the contribution rate of particles with sizes>5mm was largest to soil organic carbon, which gradually decreased with the decrease of particle size.7. The canyon karst region had strong landscape heterogeneity, meanwhile, the dominant factor was different between the ecosystems. The first five principal components cumulative contribution rate was higher than85%, which indicate the effect of dimension reduction was very good, and could fully reflect the most information. Clustering analysis showed that four groups were classified, which were (paddy field, dry land)-(grassland)(shrubbery)-(artificial forest, secondary forest). This indicated that the ecological community structure was more and more reasonable, more and more stable, along the development of groups.8. The relationship between vegetation and soil was extremely close. The strong interaction was not only reflected in the vegetation, but also reflected in the soil environmental change. For specific performance, the contribution of plants and soil microorganisms were larger, while the effect of the role of soil nutrient was relatively weaker. |
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