Abstract: Aims Rhizosphere microorganisms play an important role in plant nutrient acquisition and carbon and nitrogen cycling, and plant fine roots (including absorbing roots and transporting roots) are closely related to rhizosphere microbial communities. Elucidating the relationship between changes in fine root traits of pioneer tree species and rhizosphere microbial communities during post-fire forest restoration can provide theoretical support for post-fire vegetation restoration management based on fine roots and rhizosphere microbial dynamics. Methods The pioneer tree species Betula platyphylla was used as the research object in the 30-year time series of the burned area of Da Hinggan Mountains. The 16S rRNA high-throughput sequencing technology was used to analyze the relationship between rhizosphere bacterial community structure and soil properties and fine root traits of B. platyphylla during post-fire recovery. Important findings The results showed that post-fire recovery time significantly affected soil pH, absorptive root traits, and rhizosphere bacterial α diversity. With increasing time after fire, soil pH tended to increase, then decrease, then increase again. The specific root length and the specific root area of absorptive roots showed a trend of first increasing and then decreasing. Nine years after the fire was the turning point when the rhizosphere bacterial α diversity of B. platyphylla gradually recovered. Proteobacteria, Actinobacteriota, and Acidobacteriota were the main dominant phyla in the rhizosphere bacterial community at different post-fire recovery times, and Bradyrhizobium was the main dominant genus. Dominant genera such as Roseiarcus, Acidipila, and Mycobacterium were significantly different at different post-fire recovery times. The α diversity of rhizosphere bacteria was mainly affected by soil pH and specific root length of absorption root, and the change of bacterial community structure was affected by carbon and nitrogen content of fine roots and phosphorus content of transport roots. In conclusion, the interaction between fine roots, soil, and microorganisms jointly affects the community structure and diversity of rhizosphere bacteria, thereby shaping the rhizosphere environment and promoting ecosystem recovery after fire.

Key words: time since fire, pioneer tree species, rhizosphere, fine root traits, bacterial community