Developmental Stage Changes in Populus euphratica Alter the Rhizosphere Fungal Community Structure in Arid Environments

In arid environments, rhizosphere microbial communities change with plant developmental stages. This partly reflects the coordinated adaptation of plant-microbe interactions under stress. Our study explored the effects of Populus euphratica at different developmental stages on rhizosphere fungal communities under drought conditions. Illumina NovaSeq sequencing was performed to characterize fungal community structures across stands at different developmental stages. Significant differences in fungal α-diversity were detected among age groups. The mature developmental stage exhibited the highest species richness and diversity indices (Chao1 = 507.33, Shannon = 6.64), along with the largest proportion of unique amplicon sequence variants (ASVs, 29.04%). In contrast, the near-mature developmental stage showed the lowest values for these indicators (Chao1 = 166.62, Shannon = 4.24, unique ASVs = 6.29%). Ascomycota dominated across all developmental stages (52.36%–88.41%), whereas Basidiomycota was more abundant in over-mature and declining developmental stages (3.96%, 3.35%). Predicted functional types mainly included saprotroph, pathotroph-saprotroph and pathotroph-saprotroph-symbiotroph. The near-mature forest had the lowest co-occurrence network complexity (average degree = 9.18, total edge number = 234). The network complexity exhibited a non-monotonic pattern, characterized by a sharp decline at the near-mature developmental stage, followed by stabilization in the mature, over-mature and declining developmental stages. Fungal communities in all developmental stages exhibited deterministic assembly patterns. Partial least squares structural equation modeling (PLS-SEM) indicated that forest age correlated with soil nutrient differences. These soil nutrient differences, in turn, correlated with variations in fungal community structure. Overall, P. euphratica developmental stage was closely related to the rhizosphere microenvironment and fungal community structure. Using a space-for-time substitution approach, our study elucidated the variation patterns of rhizosphere fungal communities of P. euphratica along the forest developmental stages gradient in arid areas. Nevertheless, the mechanisms underlying temporal succession need to be further validated by long-term permanent monitoring.