Understanding the succession patterns of microbial community along root growth provides deep insights into interaction between fine roots and microbes. In the study, we investigated this issue using fine roots from poplar trees and grouped these fine roots into three growth stages: newborn white roots (WR), mature yellow roots (YR) and aging brown roots (BR). Root surface traits were observed under a scanning electron microscopy (SEM). Adhered soils on roots of the three growth stages were grouped into the three soil compartments, correspondingly. The 16S rRNA and ITS1 region were sequenced for bacteria and fungi inhabiting rhizosphere soils, respectively. Phospholipid fatty acid (PLFA) technology was employed to examine the biomass of bacterial and fungal communities. The anatomical traits of fine roots show apparent differences among the WR, YR and BR. Both bacteria and fungi have 25 dominant genera with a relative abundance over 1%, of which, both four genera of the bacteria (Bacillus, Burkholderia, Ralstonia and Dyella) differ in abundance among the WR, YR and BR soil compartments and four genera of the fungi (Fusarium, Chaetomium, Penicillium and Scleroderma) also differ in abundance among these soil compartments. The operational taxonomic units (OTUs) showed the highest richness in the WR soil compartment for bacteria and in the YR soil compartment for fungi, indicating a different succession pattern between the bacterial and fungal communities. Furthermore, the biomass of bacterial community is larger than the fungal community according to PLFAs, and both decreased along fine root growth. The total carbon (TC) in the soil increases along root growth while the dissolved organic carbon (DOC) decreases. Redundancy analysis (RDA) shows a close correlation between twelve dominant bacteria genera and the total organic carbon (TOC), the readily oxidizable organic carbon (ROC) and DOC and ten dominant fungi genera with the TOC and ROC. In conclusion, our results indicate that fine roots growth has shaped the composition and structure of root associated bacteria and fungi community.

了解根系生长过程中微生物群落的演替模式，可以深入了解细根与微生物之间的相互作用。在研究中，我们使用杨树的细根调查了这个问题，并将这些细根分为三个生长阶段：新生白根（WR），成熟黄根（YR）和衰老棕根（BR）。在扫描电子显微镜（SEM）下观察到根表面性状。将三个生长阶段的根部上附着的土壤分别分为三个土壤室。分别对根际土壤中的细菌和真菌的16S rRNA和ITS1区域进行了测序。磷脂脂肪酸（PLFA）技术用于检查细菌和真菌群落的生物量。细根的解剖特征表明WR之间存在明显差异，YR和BR。细菌和真菌都具有25个优势属，相对丰度超过1％，其中细菌的四个属（WR，YR和BR土壤区室和真菌的四个属（镰刀菌，龟皮草，青霉菌和硬皮病）之间的芽孢杆菌，伯克霍尔德氏菌，罗氏菌和狄氏菌）丰度不同）在这些土壤隔间的丰度也有所不同。可操作的生物分类单位（OTUs）在WR土壤隔间的细菌和YR土壤隔间的真菌中显示最高的丰富度，表明细菌群落和真菌群落之间的演替模式不同。此外，根据PLFAs，细菌群落的生物量大于真菌群落，并且两者均沿细根生长而下降。土壤中的总碳（TC）随着根的生长而增加，而溶解的有机碳（DOC）则减少。冗余分析（RDA）显示，十二种优势菌属与总有机碳（TOC），易氧化有机碳（ROC）和DOC以及十种优势菌属与TOC和ROC密切相关。结论，