Heavy precipitation-induced Yangtze River runoff greatly regulates heterotrophic prokaryotes production and induces P-limited growth in the northern East China Sea

초록

Although heterotrophic prokaryotes (HP) playa crucial role in biogeochemical carbon cycles, microbialoceanographic studies associated with heavy precipitation-induced large-scale freshwater runoff are understudied in theEast China Sea (ECS), the largest continental shelf in thenorthwest Pacific. To elucidate the impact of Yangtze Riverdiluted water (YRDW) on HP production (HPP) and growth-limiting resources, we conducted comprehensive microbialoceanographic measurements in combination with analysisof satellite images and optical property analyses of dissolvedorganic carbon (DOC) over three consecutive years in thenorthern ECS. Our results revealed that the HPP and chloro-phyllawere consistently highest in summer due to the sup-ply of excess DOC and nutrients via YRDW, which is intrigu-ing considering the enhanced HPP coupled with spring phy-toplankton bloom in middle latitudes in general. However,the exceptionally great YRDW runoff induced by heavy rain-fall resulted in excessive supply of terrestrial-origin recalci-trant DOC and nutrients imbalance with high N:P ratio (34),which was responsible for the limited DOC bioavailabilityand phosphorus-limitation for the HPP. Accordingly, the en-hanced HPP-to-primary production ratio (>0.5) in summermay suggest enhanced carbon flow via microbial food web,potentially altering food-web structure and energy transferefficiency. Our results, demonstrating that YRDW can ei-ther stimulate or suppress HPP, provide new insights into mi-crobial responses to large-scale freshwater discharge, whichmay be relevant to systems influenced by substantial fresh-water inputs (e.g., Amazon River and Arctic Ocean).

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