Seasonal Succession and Temperature Response Pattern of a Microbial Community in the Yellow Sea Cold Water Mass.

Explaining the temporal dynamics of marine microorganisms is critical for predicting their changing pattern under environmental disturbances. Although the effect of temperature on microbial seasonality has been widely studied, the phylogenetic structure of the temperature response pattern and the extent to which temperature shift leads to disruptive community changes are still unclear. Here, we explored the microbial seasonal dynamics in the Yellow Sea Cold Water Mass (YSCWM) that occurs in summer and disappears in winter and tested the temperature thresholds and phylogenetic coherence in response to temperature change. The existence of YSCWM generates strong temperature gradients in summer and confers little temperature change during seasonal transition, thus representing a unique intermediate state. The microbial community of YSCWM is more similar to that in the previous YSCWM in winter than that outside YSCWM. Temperature alone explains >50% of the community variation, suggesting that a temperature shift can induce a nearly seasonality-level community variance in summer. Persistence of most previous winter YSCWM inhabitants in YSCWM leads to conservation in predicted functional potentials and cooccurrence patterns, indicating a decisive role of temperature in maintaining functionality. Evaluation of the temperature threshold reveals that a small temperature change can lead to significant community turnover, with most taxa negatively responding to an elevation in temperature. The temperature response pattern is phylogenetically structured, and closely related taxa show an incohesive response. Our study provides novel insights into microbial seasonality and into how marine microorganisms respond to temperature fluctuations. IMPORTANCE Microbial seasonality is driven by a set of covarying factors including temperature. There is still a lack of understanding of the details of the phylogenetic structure and susceptibility of microbial communities in response to temperature variation. Through examination of the microbial community in a seasonally occurring summer cold water mass, which experiences little temperature change during seasonal transition, we show here that the cold water mass leads to nearly seasonality-level variations in community composition and predicted functional profile in summer. Moreover, massive community turnover occurs within a small temperature shift, with most taxa decreasing in abundance in response to increased temperature, and contrasting response patterns are observed between phylogenetically closely related taxa. These results suggest temperature as the fundamental factor over other covarying factors in structuring microbial seasonality, providing important insights into the variation mode of the microbial community under temperature disturbances.