The passive sampling hypothesis is one of the most important hypotheses used to explain the mechanism of species–area relationships (SAR) formation. This hypothesis has not yet been experimentally validated due to the confusion between passive sampling (a larger area may support more colonists when fully sampled) and sampling effects (more sampling effort will result in increased species richness when sampling is partial). In this study, we created an open microcosm system with homogeneous habitat, consistent total resources, and biodiversity background using Chinese paocai soup, a fermented vegetable, as a substrate. We made efforts to entirely exclude the influence of sampling effects and to exclusively obtain microorganisms from dispersal using microcosm and high‐throughput sequencing techniques. However, in this study, passive sampling based on dispersal failed to shape SAR, and community differences were predominantly caused by species replacement, with only minor contributions from richness differences. Ecological processes including extinction and competitive exclusion, as well as underlying factors like temporal scales and the small island effects, are very likely to have been involved in the studied system. To elucidate the mechanism of SAR development, future studies should design experiments to validate the involvement of dispersal independently.

The effect of founders (the potential influence of initially colonizing species on the composition, functionality, and stability of communities) plays a crucial role in community assembly; many experimental studies on priority effects or artificially assembled species have suggested the existence of this effect, but direct experimental evidence at the community level remains limited. This study used sterilized and nonsterilized paocai soup (a traditional Chinese fermented vegetable soup) from the same source to simulate initial environments with and without founders. These were placed in beakers with varying opening sizes on an open rooftop for 15 days to explore the impact of founders on community assembly under different dispersal intensities. The 16S rRNA sequencing analysis revealed that communities with founders exhibited lower species richness (320) compared to communities without founders (645). Additionally, communities with founders showed reduced species turnover and richness variation (53.7%) compared to communities without founders (60.9%). Furthermore, the average variability degree (AVD) in communities with founders (0.446 ± 0.044) was significantly lower than in communities without founders (0.927 ± 0.466), indicating higher community stability. Finally, deterministic processes dominated communities with founders (with heterogeneous selection contributing 70%), whereas stochastic processes primarily governed communities without founders (homogeneous dispersal 10% and undominated processes 70%). These findings demonstrate that founders presence reduces dispersal impacts, decreases community diversity, enhances stability, and deterministic processes. The effect of founders fundamentally shapes the direction of community assembly. This study helps further understanding of how founders influence biodiversity maintenance and community assembly processes.

Understanding the determinism of community succession trajectories and the factors that shape them is not only a central question in ecology, but it also bears directly on microbial management in food processing, industrial materials, and ecosystem management. Within this framework, potential differences in dispersal arising from habitat spatial structure, and how these differences vary among taxa of differing abundance, provide an important lens for examining the spatial heterogeneity of community succession. We constructed six artificial agar islands with identical area but different perimeters and boundary complexities. Using a shared microbial source and identical culture conditions, we sampled communities destructively at 16 time points from 1 to 96 h, with three independent replicates for each island × time combination (n = 288), and characterized bacterial community dynamics by 16S rRNA gene amplicon sequencing. Communities underwent continuous reorganization over 96 h, with an overall decline in ASV richness and increases in the Simpson index and Pielou evenness at later stages. Whole-community PERMANOVA showed that Time explained 51.27% of compositional variation (p < 0.001), whereas Island explained only 1.45% and was not significant (p = 0.0734); the Time × Island interaction was also not significant. Island perimeter showed no significant monotonic relationship with three successional-rate metrics or six trajectory metrics. Communities consistently retained a long-tailed abundance structure. Among 747 ASVs with detectable temporal signals, the island trajectory concordance was significantly negatively correlated with global ASV abundance rank (ρ = −0.534, p < 0.001), indicating that cross-island temporal concordance generally weakened as abundance decreased. After abundance stratification, Island was not significant for Dominant taxa (mean relative abundance ≥ 1%, p = 0.1532), but was significant for Intermediate taxa (≥0.1% and <1%, p = 0.0106) and Rare taxa (<0.1%, p < 0.001); the Time × Island interaction was significant only for the Rare stratum (p = 0.0014). Overall, time-related change constituted the major axis of whole-community variation, whereas boundary length did not generate a stable whole-community successional gradient. High-abundance members showed stronger temporal synchrony across islands, while low-abundance taxa showed greater cross-island trajectory heterogeneity. These results support a closer correspondence between shared time-related processes and synchronous changes in high-abundance core members; whether island-associated differences among low-abundance members were caused by boundary-mediated dispersal or resource exchange requires direct process measurements.

Phylogenetic diversity–habitat size relationship (PDSR), as an extension of the species–area relationship, incorporates evolutionary history to further elucidate the mechanisms shaping biogeographic patterns. However, whether PDSR is temporally unstable during community succession, and the mechanisms underlying such instability, remain poorly understood. In this study, we used a fermentation microbial community as a model and established a closed microcosm system spanning a 10–1000 mL volume gradient. By continuous sampling over 0–60 days and 16S rRNA high-throughput sequencing, we characterized the dynamic changes in PDSR throughout succession. The results showed that PDSR underwent stage-specific shifts during community succession: it was significantly positive in the early stage, weakened or became non-significant in the middle stage, and turned negative or remained non-significant in the late stage. The early positive PDSR was mainly attributable to the greater retention of rare lineages in larger-volume habitats, whereas in the late stage, phylogenetic diversity increased in smaller-volume habitats, suggesting a positive role in the resuscitation of potentially dormant lineages. Phylogenetic beta-diversity analysis further showed that lineage turnover rate increased over time, with significant divergence among samples in the later stage. In addition, pH decreased significantly over succession and, through interactions with time and volume, exerted a marked influence on community phylogenetic structure. This study reveals the temporal dynamism of biodiversity spatial patterns and confirms that PDSR shifts non-steadily across successional stages, providing new insights into the organization of microbial diversity across multiple scales.