College of Science and Engineering, James Cook University, Townsville, Queensland, Australia.
ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland, Australia.
PLoS One. 2018 Sep 21;13(9):e0203882. doi: 10.1371/journal.pone.0203882. eCollection 2018.
Phototrophic sessile organisms, such as reef corals, adjust their photosynthetic apparatus to optimize the balance of light capture versus protection in response to variable light availability (photoacclimation). In shallow marine environments, daily light integrals (DLI) can vary several-fold in response to water clarity and clouds. This laboratory study investigated the responses of two coral species to fluctuations in DLI. Corals were exposed to four contrasting DLI treatments: 'high-light' (potentially photoinhibiting conditions, 32 mol photons m-2 d-1), 'low-light' (potentially light-limiting conditions, 6 mol photons m-2 d-1), and two 'variable light' treatments that alternated between high and low conditions every 5 days. In the variable treatments, the shade-tolerant coral Pachyseris speciosa displayed cycles of rapid declines in maximum quantum yield during high-light and subsequent recoveries during low-light, showing photoacclimation at a time scale of 3-5 days. In contrast, the shallow-water coral Acropora millepora showed slow (>20 days) photoacclimation, and minimal changes in photosynthetic yields despite contrasting light exposure. However, growth (change in buoyant weight) in A. millepora was significantly slower under variable light, and even more so under low-light conditions, compared with high-light conditions. The responses of yields in P. speciosa match their preference for low-light environments, but suggest a vulnerability to even short periods of high-light exposure. In contrast, A. millepora had better tolerance of high-light conditions, however its slow photoacclimatory responses limit its growth under low and variable conditions. The study shows contrasting photoacclimatory responses in variable light environments, which is important to identify and understand as many coastal and midshelf reefs are becoming increasingly more turbid, and may experience higher variability in light availability.
光养固着生物，如珊瑚礁，会调整其光合器官以优化光捕获与保护之间的平衡，以适应可变的光可用性（光驯化）。在浅海环境中，每日积分光（DLI）可因水的清澈度和云的变化而变化数倍。本实验室研究调查了两种珊瑚对 DLI 波动的反应。珊瑚暴露于四种不同的 DLI 处理中：“高光”（潜在的光抑制条件，32 毫摩尔光子 m-2 d-1）、“低光”（潜在的光限制条件，6 毫摩尔光子 m-2 d-1）和两种“可变光”处理，每 5 天在高光和低光之间交替。在可变处理中，耐荫珊瑚 Pachyseris speciosa 在高光期间显示出快速降低最大量子产量的循环，随后在低光期间恢复，显示出在 3-5 天时间尺度上的光驯化。相比之下，浅水珊瑚 Acropora millepora 表现出缓慢（>20 天）的光驯化，尽管光照条件不同，但光合作用产量变化极小。然而，与高光条件相比，A. millepora 在可变光下的生长（浮力重量的变化）明显较慢，在低光条件下甚至更慢。P. speciosa 的产量响应与其对低光环境的偏好相匹配，但表明即使是短暂的高光暴露也会使其脆弱。相比之下，A. millepora 对高光条件的耐受性更好，但其缓慢的光驯化反应限制了其在低光和可变条件下的生长。该研究表明在可变光环境中存在相反的光驯化反应，这一点很重要，因为许多沿海和中架珊瑚礁变得越来越浑浊，并且可能经历更高的光可用性变化。
