| Rhizosphere is commonly defned as the soils where the root activity signifcantlyaffects the biological properties of soil. Due to the special environment, the rhizospheremicro-zone has become one of hot topic for the plant nutrition, plant physiology, ecologyand soil science. Because the lack of the available and comprehensive work on therhizosphere soils in the hilly loess region, the present study chose the different revegetationtypes and the vegetation community in the natural succession on the abandoned croplandto analyze the response of rhizosphere soil microorganism to the revegetation usingphospholipid fatty acids and BIOLOG carbon utilization technology. The study mainlyinvestigated the effect of revegetation types on rhizosphere soil microbial biomass,enzymes activities, microbial community structure diversity and metabolic functionaldiversity as well as the dynamic of microbial community structure diversity during theabandoned cropland for natural succession. The results could provide scientific basis forthe understanding of microbial function during the vegetation restoration. The main resultsare as follows:1. The characteristic of rhizosphere microbial properties under differentrevegetation typesSix vegetation types with8-year-old were evaluated: two artificial (i.e. planted byhumans) shrublands (Caragana korshinskii and Hippophae rhamnoides) species, twoartifcial grasslands (Astragalus adsurgens and Panicum virgatum) and two species fromcroplands that were abandoned for natural recovery (Artemisia capillaries andHeteropappus altaicus). The results showed the higher value of organic C, total N,available Mn, available Cu, available Zn, microbial biomass C, microbial biomass N,enzymes activities, microbial community structure diversity and carbon resource metabolicfunctional diversity was record for the natural grassland compared to the artificial shrublands and artificial grassland.Among the microbial properties, metabolic quotient (BR/MBC), BR, urease,water-soluble C and cellulase were found to be most important for assessing rhizospheresoil biological quality. Results of rhizosphere soil microbial index indicated that naturalgrasslands are most effective for the improvement of rhizosphere soil biological quality inthe hilly loess region, followed by the artificial grassland and artificial shrubland.A significant difference was found on the rhizosphere effect under the differentvegetation types. Natural grassland species have the significant rhizosphere effect than theartificial shrubland and artificial grassland.2. The dynamic of rhizosphere microbial properties during the abandonedcropland for natural succession.During the natural succession, the significant rhizosphere effect was only found inorganic C, total N, microbial biomass C, microbial biomass N, basal respiration, enzymesactivities and microbial community structure.Not all the microbial properties in the rhizosphere soil of dominant species werehigher than those of companion species. The higher value in the rhziosphere of dominantspecies was found in organic C, total N, microbial biomass C, microbial biomass N as wellas the metabolic on carbohydrate resources than that of companion species, while in theenzymes activities and the metabolic on carboxylic acids, the dominant species did notshowed the higher value.The successional stage of the ecosystem can significantly affect the microbialproperties in the plant rhizosphere. In the current study, the pioneer species, A. capillaries,exhibited significant fluctuations in the microbial properties, whereas the middle-latespecies, A. sacrorum, presented an increasing trend.3. The characteristics of rhizosphere microbial community structure in thenatural succession simulationThree community dominant species of the succession, A. capillaries, A. sacrorum andS. bungeana showed the significant microbial rhizosphere effect in G-negative bacterial,bacterial and total microbial biomass, their contents decreased with the increase of distancefrom root surface.At the same soil conditions, the middle-late successional species, A. sacrorum and S. bungeana had a higher rhizosphere effect of bacterial and total microbial biomass whilehad the lower G-positive bacterial and fungi rhizosphere effect than that of the pionnerspecies, A. capillaries,In the successional vegetation competition, the microbial community structurerhizosphere soil of A. capillaries and A. sacrorum and S. bungeana responded differentlyto the competition. In the competition between A. capillaries and A. sacrorum, as well asbetween A. capillaries and S. bungeana, the number of microbial PLFA of A. capillariesdid not change, while that of A. capillaries and S. bungeana decreased significantly.Furthmore, the microbial contents in the rhizopshere soil of A. capillaries was greatlyhigher than that of A. capillaries and S. bungeana.4. Allelopathic effect of dominant plants of vegetation commnutiy during theabandoned cropland for natural successionIn the seed germination experiment, an inhibition was found on the seed germinationof A. capillaries, A. sacrorum and S. bungeana with each other in their high concentrationof aqueous extracts. Furthermore, a self-allelopathic effect was observed for the seedgermination of A. capillaries. In conclusion, there is a significant alleopathic effectbetween vegetation communities during the abandoned cropland for natural succession,this effect maybe the one of the reseaons for promoting the vegetation succession in theloess hilly region. |
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