Due to climate change, the incidence of marine heat waves (MHWs) has increased, yet their effects on seaweeds are still not well understood. Adult sporophytes of Macrocystis pyrifera, the species forming the iconic giant kelp forests, can be negatively affected by thermal stress and associated environmental factors (e.g., nutrient depletion, light deprivation); however, little is known about the tolerance/vulnerability of juvenile sporophytes. Simultaneously to MHWs, juveniles can be subjected to light limitation for extended periods of time (days–weeks) due to factors causing turbidity, or even because of shading by understory canopy‐forming seaweeds. This study evaluated the effects of a simulated MHW (24°C, 7 d) in combination (or not) with light deprivation, on the photosynthetic capacities, nutrient uptake, and tissue composition, as well as oxidative stress descriptors of M. pyrifera juvenile sporophytes (single blade stage, up to 20 cm length). Maximum quantum yield (F_v/F_m) decreased in juveniles under light at 24°C, likely reflecting some damage on the photosynthetic apparatus or dynamic photoinhibition; however, no other sign of physiological alteration was found in this treatment (i.e., pigments, nutrient reserves and uptake, oxidative stress). Photosynthetic capacities were maintained or even enhanced in plants under light deprivation, likely supported by photoacclimation (pigments increment); by contrast, nitrate uptake and internal storage of carbohydrates were strongly reduced, regardless of temperature. This study indicated that light limitation can be more detrimental to juvenile survival, and therefore recruitment success of M. pyrifera forests, than episodic thermal stress from MHWs.

中文翻译：

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热浪和光剥夺对巨型海带少年（Macrocystis pyrifera，Laminariales，Phaeophyceae）的影响。

由于气候变化，海洋热浪（MHW）的发生率增加了，但对海藻的影响仍未得到很好的了解。萤火虫大孢子虫的成年孢子体，形成标志性巨型海带森林的物种可能会受到热应力和相关环境因素（例如养分耗竭，光剥夺）的负面影响；然而，关于幼年孢子体的耐受性/脆弱性知之甚少。与MHW同时，由于引起浑浊的因素，甚至由于下层冠层形成的海藻产生的阴影，幼鱼可能会长时间（几天-几周）受到光照限制。这项研究评估了模拟的MHW（24°C，7 d）结合（或不结合）光剥夺对拟南芥幼虫的光合能力，养分吸收和组织组成以及氧化应激指标的影响。孢子体（单叶片阶段，最大20厘米长）。最大的量子产率（˚F_v / F _m）在24°C光照下的少年中下降，可能反映了对光合作用装置的某些破坏或动态光抑制作用；然而，在该处理中没有发现其他生理变化的迹象（即色素，养分储备和吸收，氧化应激）。在光剥夺条件下，植物的光合能力得以维持甚至增强，这很可能受到光适应（色素增加）的支持；相比之下，无论温度如何，硝酸盐的吸收和碳水化合物的内部存储都会大大降低。这项研究表明，与MHWs引起的间歇性热胁迫相比，光限制可能对幼虫的存活更加有害，因此对招生的M. pyrifera森林招募成功更大。