Institute of Biochemistry and Biology, University of Potsdam, Am Neuen Palais 10, 14469, Potsdam, Germany.
Oecologia. 2012 Jul;169(3):609-22. doi: 10.1007/s00442-011-2225-4. Epub 2011 Dec 28.
In the deep, cooler layers of clear, nutrient-poor, stratified water bodies, phytoplankton often accumulate to form a thin band or "deep chlorophyll maximum" (DCM) of ecological importance. Under such conditions, these photosynthetic microorganisms may be close to their physiological compensation points and to the boundaries of their ecological tolerance. To grow and survive any resulting energy limitation, DCM species are thought to exhibit highly specialised or flexible acclimation strategies. In this study, we investigated several of the adaptable ecophysiological strategies potentially employed by one such species, Chlamydomonas acidophila: a motile, unicellular, phytoplanktonic flagellate that often dominates the DCM in stratified, acidic lakes. Physiological and behavioural responses were measured in laboratory experiments and were subsequently related to field observations. Results showed moderate light compensation points for photosynthesis and growth at 22°C, relatively low maintenance costs, a behavioural preference for low to moderate light, and a decreased compensation point for photosynthesis at 8°C. Even though this flagellated alga exhibited a physiologically mediated diel vertical migration in the field, migrating upwards slightly during the day, the ambient light reaching the DCM was below compensation points, and so calculations of daily net photosynthetic gain showed that survival by purely autotrophic means was not possible. Results suggested that strategies such as low-light acclimation, small-scale directed movements towards light, a capacity for mixotrophic growth, acclimation to low temperature, in situ exposure to low O(2), high CO(2) and high P concentrations, and an avoidance of predation, could combine to help overcome this energetic dilemma and explain the occurrence of the DCM. Therefore, corroborating the deceptive ecophysiological complexity of this and similar organisms, only a suite of complementary strategies can facilitate the survival of C. acidophila in this DCM.
在清澈、营养贫乏、分层的水体的较深、较冷的层中，浮游植物经常聚集形成一个薄带或“深层叶绿素最大值”（DCM），具有重要的生态意义。在这种情况下，这些光合微生物可能接近其生理补偿点和生态耐受极限。为了克服由此产生的能量限制而生长和存活，人们认为 DCM 物种表现出高度专门化或灵活的适应策略。在这项研究中，我们研究了一种此类物种——嗜酸小球藻（Chlamydomonas acidophila）可能采用的几种适应性生理策略：一种运动、单细胞、浮游植物鞭毛藻，它经常在分层、酸性湖泊中主导 DCM。在实验室实验中测量了生理和行为反应，然后将其与野外观察相关联。结果表明，在 22°C 下光合作用和生长的中等光补偿点、相对较低的维持成本、对低至中等光的行为偏好以及在 8°C 下光合作用补偿点降低。尽管这种有鞭毛的藻类在野外表现出生理介导的昼夜垂直迁移，在白天稍微向上迁移，但到达 DCM 的环境光低于补偿点，因此光合作用的每日净增益计算表明，仅通过自养方式生存是不可能的。结果表明，低光照适应、朝向光的小规模定向运动、混合营养生长的能力、低温适应、原位暴露于低 O2、高 CO2 和高 P 浓度以及避免捕食等策略可以结合起来帮助克服这种能量困境，并解释 DCM 的发生。因此，证实了这种和类似生物体具有欺骗性的生理复杂性，只有一系列互补的策略才能促进嗜酸小球藻在这种 DCM 中的生存。
