P-limited Prokaryotic Heterotrophic Production and Metabolic Balance Between Prokaryotic Carbon Demand and Phytoplankton Primary Production in Summer in the Central Yellow Sea

Abstract

We investigated the spatial distribution of prokaryotic heterotrophic production (PHP), its limiting resources, and the metabolic balance between prokaryotic carbon demand (PCD) and primary production (PP) in summer in the central Yellow Sea (YS). Due to the formation of strong stratification, the water column was divided vertically into two water masses: nutrient-poor and high-temperature Yellow Sea Surface Water (YSSW) and nutrient-rich and low-temperature Yellow Sea Cold Bottom Water, and the YSSW was further divided into northern and southern part. In the northern YSSW, where dissolved organic carbon (DOC) concentration was higher, relatively higher PHP and prokaryotic respiration (PR) were observed compared to the southern YSSW. However, despite the high DOC concentration and lability of dissolved organic matter, PHP and PR were relatively lower than those reported in coastal YS. Limiting resource incubation experiments demonstrated that PHP was stimulated in samples amended with P, which suggested that prokaryotic growth was restricted by P deficiency. The P-limited PHP in high DOC condition suggested that P deficiency for prokaryotic growth would inhibit prokaryotic organic carbon uptake, leading to DOC accumulation in the surface layer. The metabolic balance appeared to be autotrophy (PCD:PP < 1) in the mixed layer, and strong stratification might prevent the CO2 accumulated below the thermocline from moving to the surface. Overall results imply that when P deficiency due to the physical structure of the water column limits prokaryotic growth in the central YS in summer, net autotrophy may occur. © The Author(s), under exclusive licence to Korea Institute of Ocean Science & Technology (KIOST) and the Korean Society of Oceanography (KSO) and Springer Nature B.V. 2025.