Distinct temporal patterns and processes of abundant and rare DOM molecules

Temporal-scale patterns and the underlying ecological mechanisms of microbial communities have been extensively investigated in microbial ecology. However, the understanding of the closely related temporal patterns of dissolved organic matter (DOM) remains limited. To address this knowledge gap, we conducted a year-long study to examine the classic temporal-scale patterns, namely the time-decay relationship (TDR) and species-time relationship (STR), of DOM pools, bacterial, and fungal communities in the intertidal zone. Our findings indicate that DOM exhibits similar temporal-scale patterns as microbial communities, albeit with weaker temporal turnover. The temporal patterns across DOM, bacterial, and fungal communities are primarily driven by rare molecules or taxa. Specifically, molecules with lower mass and higher molecular polarity contribute to TDR patterns, while those with higher mass and lower molecular polarity drive STR patterns. Furthermore, the SparCC co-occurrence ecological network reveals the temporal dynamics of the main DOM modules, with most modules exhibiting the lowest eccentricity in April. Null model and variance partitioning analyses indicate that deterministic processes govern the assembly of the entire and rare DOM pools, as well as bacterial and fungal communities, while stochastic processes dominate abundant DOM pools and bacterial and fungal sub-communities. These results provide support for the “size-dispersal” hypothesis, emphasizing the crucial role of individual size and dispersal in the assembly of DOM and microbial communities. Moreover, the study underscores the importance of “rare molecular assemblages”, an ancient assemblage that potentially harbors substantial chemodiversity. By shedding light on the ecological mechanisms of intertidal DOM, this study deepens our understanding of microbial-driven chemical ecology.