海洋升温与磷限制对海带(Saccharina japonica)生长与光合性能的影响*

Effects of ocean warming and phosphorus limitation on the growth and photosynthesis of Saccharina japonica

摘要:

海带(Saccharina japonica)是一类重要的海洋资源，在食物供给、近岸生态系统修复与蓝碳固存方面发挥关键作用。海洋升温与磷限制均可显著改变海带的生长、繁殖与生态系统功能，但二者的联合作用和交互机制仍不清楚。本研究在实验室受控条件下，设置了五个温度梯度(2、5、10、15 和 18 ℃)和两个磷水平处理(磷充足：N:P=10:1；磷限制：N:P=100:1)，旨在定量评估海带生长与光合性能对温度和磷限制的响应。结果显示升温显著增强了海带生长、净光合速率与总光合速率(p<0.05)，并提高了光捕获能力与光合效率，其中10–15 ℃ 的促进效应最强。相反，磷限制显著抑制了海带的生长与光合性能(p<0.05)，并重构光捕获与光保护机制，具体表现为叶绿素 a 与岩藻黄素含量、PSII 最大光化学效率、有效量子产额与最大电子传递速率均下降，而非光化学猝灭(NPQ)升高，表明能量分配由光能利用转向了光保护。升温限制加剧了磷限制的这些负面影响，温度与磷限制有交互作用，在高温条件下磷限制对生长与光合能力的抑制最为显著(p<0.05)。碳浓缩机制和卡尔文循环酶活性虽有所增强以部分补偿光合限制，但仍难以完全抵消升温和磷限制的双重胁迫影响。本研究揭示了温度与磷供应均会对海带生长及光合作用产生影响且两者具有交互作用，为理解海带在全球变暖和营养限制背景下的生理适应提供了基础科学依据；同时，这些发现提示未来海洋变暖情况下，磷供应不足可能降低海带养殖系统的净初级生产力与蓝碳固存潜力，因此评估海带生态功能与碳汇贡献时应同时考虑变暖趋势与营养盐配比失衡。

Abstract:

Kelp is a valuable resource that plays vital roles in food supply, coastal ecosystem restoration, and blue carbon sequestration. Ocean warming and phosphorus limitation substantially alter the growth, reproduction, and ecosystem functions of kelp; however, their combined effects remain unclear. Here, we conducted controlled laboratory experiments to quantitatively assess the effects of ocean warming (2, 5, 10, 15, and 18 °C) and phosphorus limitation (replete, N:P = 10:1; limited, N:P = 100:1) on the growth and photosynthetic performance of Saccharina japonica. Warming enhanced S. japonica growth, net photosynthesis, and gross photosynthesis (p < 0.05), and improved light-harvesting and photosynthetic efficiency, with the strongest stimulation at 10–15 °C. Conversely, phosphorus limitation suppressed growth and photosynthetic performance (p < 0.05) and reconfigured the light-harvesting and photoprotective machinery. Specifically, chlorophyll a and fucoxanthin content, maximum photochemical efficiency, effective quantum yield, and maximum electron transport rate decreased, whereas non-photochemical quenching increased, indicating a shift from light utilisation to photoprotection. Warming and phosphorus limitation amplified the negative effects, with the inhibition of growth and photosynthetic capacity being strongest under high temperature (p < 0.05). Although carbon-concentrating mechanisms and activities of Calvin cycle enzymes were up-regulated and provided partial compensation, they did not fully offset the dual stress. This study demonstrates that both temperature and phosphorus availability significantly influence the growth and photosynthetic performance of Saccharina japonica, and that these factors interact to shape its physiological responses, thereby providing a mechanistic basis for understanding kelp acclimation under concurrent ocean warming and nutrient limitation. Moreover, our findings suggest that, under future warming scenarios, insufficient phosphorus supply may reduce net primary productivity and blue-carbon sequestration potential in kelp aquaculture systems; therefore, assessments of kelp ecological function and carbon-sink contributions should explicitly account for both warming trends and nutrient-stoichiometric imbalance.