Narvarte Bienson Ceasar V, Mendoza Emmanuel M, Gacura Jonh Rey L, Hinaloc Lourie Ann R, Roleda Michael Y
Algal Ecophysiology Laboratory, College of Science, The Marine Science Institute, University of the Philippines, Diliman, 1101, Quezon City, Philippines.
Bolinao Marine Laboratory, UPMSI, Guiguiwanen, Luciente 1, Bolinao, Pangasinan, Philippines.
Planta. 2025 Mar 27;261(5):96. doi: 10.1007/s00425-025-04673-6.
Eucheumatoids exhibited significant day and night nutrient uptake, with NH increasing linearly, NO following Michaelis-Menten kinetics, higher internal NH, NO, PO at night, and peak nitrate reductase activity during day. Nutrient physiology of aquatic phototrophs is mostly measured during daytime or experimentally under saturating irradiance with the assumption that nutrient uptake is tightly coupled with photosynthetic activities. At night or under dark condition, when photosynthesis ceases, little is known on the nutrient physiology of these macrophytes. Here, we examined the nutrient uptake of commercially important eucheumatoids Kappaphycus alvarezii, K. striatus, and Eucheuma denticulatum during night and daytime, considering conditions that extend beyond just the presence or absence of light. The NH and NO uptake of the three eucheumatoid species were higher during the day (53.4-58.2% of the total TIN absorbed), although nighttime uptake (41.8-46.6% of the total TIN absorbed) also contributed significantly to the overall uptake rates. For both night and daytime, the NH uptake of the three eucheumatoid species increased linearly with the substrate concentration while NO uptake followed the Michaelis-Menten saturation kinetics. Higher V were observed for K. striatus (5.670 ± 0.474 µmol h g DW) and E. denticulatum (8.058 ± 1.632 µmol h g DW) during nighttime, while nighttime K values of the three species (13.028-32.387 µM) were higher compared to their daytime values (6.397-9.238 µM). Regardless of night- or day-sampling time, the nutrient (NH, NO, NO and PO) concentration in the seaweeds' internal pools were higher than their concentrations in the surrounding seawater, highlighting their capacities to store inorganic nutrients. Higher amounts of NH, NO and PO in the seaweeds' internal pools were observed during nighttime while NO in the internal pools were similar at both periods. Lastly, the three eucheumatoid species exhibited higher nitrate reductase activities (NRAs) during the day. Our study showed that algal nutrient uptake and nitrogen metabolism are independent of light and photosynthesis. Understanding the influence of night and daytime in nutrient uptake can provide insights in the sustainable nutrient management for commercial crop production and/or in incorporating eucheumatoids in an integrated multi-trophic aquaculture (IMTA) system. In terms of accounting for the bioremediation potentials of the above species, it is important to measure both nighttime and daytime nutrient uptakes.
麒麟菜表现出显著的昼夜养分吸收，铵（NH）呈线性增加，硝酸盐（NO）遵循米氏动力学，夜间内部的NH、NO、磷酸盐（PO）含量更高，白天硝酸盐还原酶活性达到峰值。水生光合生物的养分生理学大多是在白天测量的，或者是在饱和光照条件下通过实验测量的，假设养分吸收与光合作用活动紧密相关。在夜间或黑暗条件下，当光合作用停止时，对于这些大型海藻的养分生理学了解甚少。在此，我们研究了具有商业重要性的麒麟菜、锯齿麒麟菜和细齿麒麟菜在夜间和白天的养分吸收情况，考虑的条件不仅仅是有无光照。这三种麒麟菜的NH和NO吸收在白天较高（占总溶解性无机氮（TIN）吸收量的53.4 - 58.2%），尽管夜间吸收（占总TIN吸收量的41.8 - 46.6%）对总体吸收速率也有显著贡献。对于夜间和白天而言，这三种麒麟菜的NH吸收随底物浓度呈线性增加，而NO吸收遵循米氏饱和动力学。在夜间，锯齿麒麟菜（5.670 ± 0.474 μmol h g DW）和细齿麒麟菜（8.058 ± 1.632 μmol h g DW）观察到较高的最大吸收速率（V），而这三个物种的夜间米氏常数（K）值（13.028 - 32.387 μM）高于其白天的值（6.397 - 9.238 μM）。无论夜间还是白天的采样时间，海藻内部池中的养分（NH、NO、亚硝酸盐（NO）和PO）浓度都高于其周围海水中的浓度，突出了它们储存无机养分的能力。夜间在海藻内部池中观察到较高量的NH、NO和PO，而两个时期内部池中的NO相似。最后，这三种麒麟菜在白天表现出较高的硝酸盐还原酶活性（NRAs）。我们的研究表明，藻类的养分吸收和氮代谢与光照和光合作用无关。了解昼夜对养分吸收的影响可以为商业作物生产的可持续养分管理和/或将麒麟菜纳入综合多营养层次水产养殖（IMTA）系统提供见解。就考虑上述物种的生物修复潜力而言，测量夜间和白天的养分吸收都很重要。
