Department of Marine Sciences, University of Gothenburg, SE 405 30, Gothenburg, Sweden.
WEAQ AB, Doktorsgatan 9D, Ängelholm, Sweden.
Sci Rep. 2019 Feb 5;9(1):1424. doi: 10.1038/s41598-018-38059-4.
Growth of large phytoplankton is considered to be diffusion limited at low nutrient concentrations, yet their constraints and contributions to carbon (C) and nitrogen fluxes in field plankton communities are poorly quantified under this condition. Using secondary ion mass spectrometry (SIMS), we quantified cell-specific assimilation rates of C, nitrate, and ammonium in summer communities of large phytoplankton when dissolved inorganic nitrogen concentrations are low in temperate coastal regions. Chain-forming diatoms composed 6% of total particulate organic carbon, but contributed 20% of C assimilation, 54% of nitrate assimilation and 32% of ammonium assimilation within the plankton community. In contrast, large dinoflagellates composed 11% of total POC, and contributed 14% of the C assimilation, 4% of ammonium and 9% of nitrate assimilation within the plankton community. Measured cell-specific C and nitrate assimilation rate match the Redfield ratio and the maximal nitrate assimilation in Chaetoceros spp. predicted by mass transfer theory. However, average ammonium assimilation rates were 30 and 340% higher than predicted by mass transfer theory in Tripos/Ceratium and Chaetoceros, respectively, suggesting that microbial interactions in the phycosphere may facilitate substantial luxury ammonium uptake by Chaetoceros in environments with fluctuating nitrate concentrations.
在营养物质浓度较低的情况下，大型浮游植物的生长被认为是扩散限制的，但在这种条件下，它们对浮游植物群落中碳（C）和氮通量的限制和贡献在野外条件下还没有得到很好的量化。本研究使用二次离子质谱（SIMS），在温带沿海地区溶解无机氮浓度较低的情况下，对夏季大型浮游植物群落中 C、硝酸盐和铵盐的细胞特异性同化率进行了定量。在浮游植物群落中，链状硅藻占总颗粒有机碳的 6%，但同化了 20%的 C、54%的硝酸盐和 32%的铵盐。相比之下，大型甲藻占总 POC 的 11%，同化了浮游植物群落中 14%的 C、4%的铵盐和 9%的硝酸盐。测量的细胞特异性 C 和硝酸盐同化率与红场比和质量传递理论预测的 Chaetoceros spp. 的最大硝酸盐同化率相匹配。然而，在 Tripos/Ceratium 和 Chaetoceros 中，平均铵盐同化率分别比质量传递理论预测值高出 30%和 340%，这表明在硝酸盐浓度波动的环境中，浮游植物圈内的微生物相互作用可能促进了 Chaetoceros 大量奢侈性铵盐的吸收。
