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https://doi.org/10.5194/egusphere-2025-4047
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-4047
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
19 Sep 2025
| 19 Sep 2025
Status: this preprint is open for discussion and under review for Biogeosciences (BG).
Role of phosphorus concentration and the nitrogen to phosphate ratio in the synergistic stimulation of alkaline phosphatase activity in Laizhou Bay, China, coastal waters
Abstract. In coastal ecosystems, microbial alkaline phosphatase (AP) production is primarily induced by low phosphate (PO4-P) availability but is additionally regulated by the dissolved inorganic nitrogen to phosphate (DIN:PO4-P) ratio and seasonal temperature variation. However, the dominant driver of APA surges and potential synergistic effects among these factors remain unclear. Through integrated seasonal field surveys and an enclosure experiments in Laizhou Bay, China, we demonstrate that PO4-P seawater concentration serves as the primary control for APA induction, with a consistent threshold of 0.05 . Below this threshold, APA exhibits a significant positive correlation with the DIN:PO4-P ratio in both the field and an enclosure experiment under P limitation (combined analysis of field and experimental data, p＜0.01; n=36). Notably, phytoplankton-dominated APA is evidenced in autumn. Genetic analysis confirms that AP-related gene expression increases only when PO4-P falls below the identified threshold. These findings refine the conceptual framework for AP regulation in coastal ecosystems, highlighting the hierarchical control of phosphorus limitation over stoichiometric effects.
How to cite. Yang, Y., Duan, X., Liang, S., Zhang, M., Li, S., Li, H., Zhang, G., Ma, H., Han, X., and Wang, X.: Role of phosphorus concentration and the nitrogen to phosphate ratio in the synergistic stimulation of alkaline phosphatase activity in Laizhou Bay, China, coastal waters, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-4047, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Yanqun Yang
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
National Marine Environmental Monitoring Center, State Oceanic Administration, Dalian 116023, China
Xiaomeng Duan
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Shengkang Liang
CORRESPONDING AUTHOR
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Mingzheng Zhang
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Marine Science Research Institute of Shandong Province
Shanshan Li
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Hongguan Li
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Guoling Zhang
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Haoyang Ma
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Xiurong Han
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Xiulin Wang
Key Laboratory of Marine Chemistry Theory and Technology, Ministry of Education / Innovation Center for Ocean Carbon Neutrality, Ocean University of China, Qingdao 266100, China
College of Chemistry and Chemical Engineering, Ocean University of China, Qingdao 266100, China
Short summary
Coastal bays face nitrogen increases while phosphorus stays scarce. At <0.05 μmol/L phosphorus, marine microbes boost alkaline phosphatase production. The nitrogen:phosphorus ratio further enhances this when phosphorus is limited. Our research reveals how nutrient imbalances favor phosphorus-adapted organisms, reshaping ecosystems. Better nutrient management is needed to protect coastal waters.
Coastal bays face nitrogen increases while phosphorus stays scarce. At <0.05 μmol/L phosphorus,...
This manuscript presents a comprehensive investigation by land-sea synchronous field surveys and enclosure experiments to reveal the potential regulatory mechanisms of alkaline phosphatase activity (APA) in the coastal waters of Laizhou Bay (LZB). The authors proved that the absolute phosphate (PO₄-P) concentration and the ratio nitrogen-to-phosphate ratio (DIN:PO₄-P) have synergistic effects on regulation of the APA secretion and organophosphorus utilization. The combination of geochemical measurements and molecular biological evidence provides valuable insights into phosphorus cycling driven by anthropogenic nitrogen inputs in coastal zones of LZB.
Overall, this is a well-structured and well-supported manuscript that meets the standards for publication. However, several issues should be addressed or clarified to further strengthen the manuscript.
Figure 3 shows a spatial overlap between areas of high Chl a concentration and high APA, particularly near the Xiaoqing River (XQR) and Yellow River (YR) estuaries. It is suggested to explicitly point out this coupling relationship in Section 3.2 or 3.3 of the Results. For example, adding a sentence like: "Notably, the spatial distributions of high Chl a concentrations and high APA_total values showed remarkable consistency, especially in the adjacent areas of the XQR and YR estuaries." This would visually strengthen the conclusion that phytoplankton biomass is an important driver of APA.
The study identifies a distinct PO₄-P threshold (0.05 μmol·L⁻¹), which is well-supported by data from autumn and the enclosure experiment. However, the winter data show no significant correlation between APA and either PO₄-P or the DIN:PO₄-P ratio. It is recommended that the authors further discuss the potential reasons for this seasonal discrepancy in the discussion section. For instance, is it due to direct suppression of microbial activity and enzyme production by low winter temperatures, or does the phytoplankton community structure in winter (e.g., potentially diatom-dominated) inherently respond differently to P stress compared to summer/autumn communities? A deeper analysis of these factors would help clarify the boundary conditions under which the "threshold" concept applies.
The manuscript states that APA in autumn was primarily derived from phytoplankton. Could the authors briefly discuss the potential role of the dominant species (e.g., specific genera within diatoms) or functional groups (e.g., groups known to strongly induce APA under P stress) present in the phytoplankton community during that season? Even in the absence of species-level data, referencing existing literature on which common taxa tend to exhibit high APA under P stress would make the conclusion of "phytoplankton-dominated APA" more concrete and enriched.
The study measured the enzyme kinetic parameters Km and Vmax and observed their changes below the identified threshold. It is recommended that the discussion include an explanation of the ecological implications of these parameter changes using more intuitive ecological terminology. For instance, a decrease in Km may indicate enhanced enzyme affinity for the substrate, representing an adaptive strategy under low-phosphorus conditions. Adding such an explanation would make these biochemical parameters more accessible to a broader audience of ecologists, thereby enhancing the readability and impact of the manuscript.
The MS is generally well-writton, but still need improve language clarity and fluency. Some sentences are unnecessarily long or awkwardly phrased.
In Figure 6, the scatter plot in the lower panel demonstrates a positive correlation between APA and the DIN:PO₄-P ratio, distinguishing between "high APA" and "low APA" groups. It would be beneficial to briefly state in the figure caption or main text the criterion used to separate these two groups (e.g., based on a specific APA value, or using a statistical clustering method). This would enhance the transparency of the analytical approach.
Recommendation
Minor revision. The manuscript is timely, novel, and well-supported by data, but the above points should be addressed to improve scientific rigor, clarity, and broader impact.