【 Objective】 This study aims to explore the influence of soil microorganisms on the rhizosphere microbiota characteristics of Caragana korshinskii under nitrogen deposition background, and explore the regulatory rules of microbiota changes on the morphological construction of C. korshinskii root system, so as to provide theoretical basis for ecological restoration of fragile ecosystems.【Method】On the basis of soil sterilization treatment (sterilized soil (+S) and non-sterilized soil (-S)), 1-year-old potted C. korshinskii seedlings were subjected to two kinds of inoculation experiments (mixed inoculation with Rhizophagus intraradices and Funneliformis mosseae (+M), and non-inoculation treatment (−M)), and three nitrogen addition treatments (no nitrogen application (0N, 0 g·m−2a−1), low nitrogen (LN, 3 g·m−2a−1), high nitrogen (HN, 6 g·m−2a−1)). After the end of the growing season, the soil microbial biomass, soil enzymes activity related to nutrient conversion, soil nutrient content, and seedling fine root morphology with diameter ≤ 0.5 mm (total root length, total surface area, total volume and number of root tips) of each treatment were analyzed, the correlation between micro ecological environment changes and root morphology construction was explored.【 Result】 1) In both 0N and LN treatments, the microbial biomass carbon content in rhizosphere soil of C. korshinskii in non-sterilized soil was higher than that in sterilized soil. In HN treatment, the soil microbial biomass carbon content of non-mycorrhizal seedlings was the lowest in sterilized soil. In sterilized soil with different nitrogen addition treatments, the activity of carbon conversion related enzymes in rhizosphere soil of mycorrhizal seedlings was higher than that of non-mycorrhizal seedlings (P<0.05), while the soluble carbon content in rhizosphere soil of C. korshinskii in non-sterilized soil and inoculation treatment was higher than that in the single treatment (P<0.05). 2) Under different nitrogen addition treatments, the nitrogen content of rhizosphere soil microbial biomass of non-mycorrhizal seedlings of C. korshinskii in non-sterilized soil treatment was significantly higher than that in sterilized soil treatment (P<0.05), and the activity of nitrogen conversion related enzymes in rhizosphere soil of C. korshinskii in the interaction of non-sterilized soil treatment and inoculation treatment was significantly higher than that in the single treatment. Under LN and HN treatments, the rhizosphere available nitrogen content of non-mycorrhizal seedlings in soil sterilization was significantly higher than that in other treatments (P<0.05). 3) Under HN treatment, the phosphorus content and alkaline phosphatase activity of microbial biomass in rhizosphere soil of C. korshinskii in the interaction of non-sterilized soil and inoculation treatment were significantly higher than those in other treatments (P<0.05), and the available phosphorus content in rhizosphere soil in the interaction of non-sterilized soil and inoculation treatment was between the single effects of non-sterilized soil and inoculation treatment. 4) Under HN treatment, the root morphological indexes of C. korshinskii mycorrhizal seedlings in sterilized soil were the highest. Under 0N treatment, the root morphological indexes of non-mycorrhizal seedlings in non-sterilized soil were the smallest. 5) The redundancy analysis results showed that microbial biomass carbon content had the highest explanatory degree in the key regulatory factors affecting the root morphology of seedlings, and it had a positive regulatory effect. The results of multiple linear regression analysis showed that alkaline phosphatase activity had the greatest influence on seedling root morphology, and it showed a negative regulatory effect.【Conclusion】Under the background of exogenous nitrogen input, the synergistic effect of non-sterilized soil treatment and seedling inoculation treatment is conducive for maintaining the balance of plant rhizosphere microhabitat, and the limiting factor of rhizosphere microhabitat in high nitrogen treatment is transformed into phosphorus element. The root growth of C. korshinskii seedling is promoted by inoculation treatment, but is restricted by soil sterilization treatment. The root growth is closely related to soil carbon and phosphorus cycles process. The root morphological construction is positively regulated by boil microbial biomass, but it is negatively regulated by phosphorus transformation related enzymes. © 2024 Chinese Society of Forestry. All rights reserved.
