Departamento de Ecología, Facultad de Ciencias, Universidad de Granada, Campus Fuentenueva s/n, Granada, 18071, España.
Instituto Universitario de Investigación del Agua, Universidad de Granada, C/Ramón y Cajal, 4, Granada, 18071, España.
New Phytol. 2019 Feb;221(3):1317-1327. doi: 10.1111/nph.15470. Epub 2018 Oct 11.
Mixotrophy is a dominant metabolic strategy in ecosystems worldwide. Shifts in temperature (T) and light (i.e. the ultraviolet portion of spectrum (UVR)) are key abiotic factors that modulate the conditions under which an organism is able to live. However, whether the interaction between both drivers alters mixotrophy in a global-change context remains unassessed. To determine the T × UVR effects on relative electron transport rates, nonphotochemical quenching, bacterivory, and bacterial production, we conducted an experiment with Isochrysis galbana populations grown mixotrophically, which were exposed to 5°C of cooling and warming with respect to the control (19°C) with (or without) UVR over light-dark cycles and different timescales. At the beginning of the experiment, cooling inhibited the relative electron transport and bacterivory rates, whereas warming depressed only bacterivory regardless of the radiation treatment. By the end of the experiment, warming and UVR conditions stimulated bacterivory. These reduced relative electron transport rates (c. 50% (warming) and > 70% (cooling)) were offset by increased (35%) cumulative bacterivory rates under warming and UVR conditions. We propose that mixotrophy constitutes an energy-saving and a compensatory mechanism to gain carbon (C) when photosynthesis is impaired, and highlight the need to consider the natural environmental changes affecting the populations when we test the impacts of interacting global-change drivers.
混养是全球生态系统中占主导地位的代谢策略。温度（T）和光照（即光谱的紫外线部分（UVR））的变化是调节生物生存条件的关键非生物因素。然而，这两个驱动因素的相互作用是否会在全球变化背景下改变混养状态尚未得到评估。为了确定 T 和 UVR 对相对电子传递率、非光化学猝灭、噬菌作用和细菌生产力的影响，我们进行了一项实验，使用异养小球藻种群进行混养，这些种群在光照-暗周期和不同时间尺度下经历了相对于对照（19°C）的冷却（5°C）和加热（5°C），同时伴有或不伴有 UVR。在实验开始时，冷却抑制了相对电子传递率和噬菌作用率，而加热仅抑制了噬菌作用率，而不论辐射处理如何。在实验结束时，加热和 UVR 条件刺激了噬菌作用。这些相对电子传递率的降低（加热时约为 50%，冷却时大于 70%）被加热和 UVR 条件下累积噬菌作用率的增加（35%）所抵消。我们提出，混养是一种节能和补偿机制，当光合作用受到损害时，可以获得碳（C），并强调在测试相互作用的全球变化驱动因素的影响时，需要考虑影响种群的自然环境变化。
