Diverse microbial communities support multiple patterns of functional redundancy in tidal flats across the Chinese coastline

Abstract

Tidal flats are critical transitional ecosystems in which microbial communities drive essential biogeochemical processes while adapting to strong environmental fluctuations. However, the mechanisms by which these communities maintain functional stability in highly dynamic tidal-flat environments remain poorly understood. In this study, we analyzed 276 tidal-flat samples from 92 coastal sites along the Chinese coastline to investigate the relationship between microbial diversity and community function. Our results revealed significant spatial variability in microbial communities across different regions of the Chinese coastline. Although latitude and geographic distance had detectable effects, the community turnover was governed primarily by environmental filtering and stochastic assembly, with temperature emerging as a key environmental driver. Despite the great variation in species diversity, the relatively similar functions of microbial communities across different regions were observed, indicating the existence of functional redundancy. Using a novel framework to quantify how the redundancy varies across microbial functions and communities, we illuminated the redundancy order of major biogeochemical functions in tidal flats as carbon > sulfur > nitrogen metabolism. We also identified three distinct redundancy patterns: high-, low-, and latitude-associated redundancy. By identifying the contributor composition underlying each function, we further revealed that the functional redundancy in tidal-flat ecosystems was shaped by the distribution of functional genes across microbial lineages, and that shifts in the balance between generalists and specialists helped explain the observed diversity of redundancy patterns. This study provides a quantitative framework for delineating microbial functional redundancy and its underlying contributor composition. By applying this framework to tidal flats along the Chinese coastline across four climatic zones, we revealed distinct patterns of functional redundancy and illuminated that a shift in the primary functional contributor would alter the redundancy pattern. These findings underscore the critical role of contributor composition in determining the stability and resilience of tidal-flat microbiomes. Video Abstract