Table_1_It Is Hot in the Sun: Antarctic Mosses Have High Temperature Optima for Photosynthesis Despite Cold Climate.docx

The terrestrial flora of Antarctica’s frozen continent is restricted to sparse ice-free areas and dominated by lichens and bryophytes. These plants frequently battle sub-zero temperatures, extreme winds and reduced water availability; all influencing their ability to survive and grow. Antarctic mosses, however, can have canopy temperatures well above air temperature. At midday, canopy temperatures can exceed 15°C, depending on moss turf water content. In this study, the optimum temperature of photosynthesis was determined for six Antarctic moss species: Bryum pseudotriquetrum, Ceratodon purpureus, Chorisodontium aciphyllum, Polytrichastrum alpinum, Sanionia uncinata, and Schistidium antarctici collected from King George Island (maritime Antarctica) and/or the Windmill Islands, East Antarctica. Both chlorophyll fluorescence and gas exchange showed maximum values of electron transport rate occurred at canopy temperatures higher than 20°C. The optimum temperature for both net assimilation of CO2 and photoprotective heat dissipation of three East Antarctic species was 20–30°C and at temperatures below 10°C, mesophyll conductance did not significantly differ from 0. Maximum mitochondrial respiration rates occurred at temperatures higher than 35°C and were lower by around 80% at 5°C. Despite the extreme cold conditions that Antarctic mosses face over winter, the photosynthetic apparatus appears optimised to warm temperatures. Our estimation of the total carbon balance suggests that survival in this cold environment may rely on a capacity to maximize photosynthesis for brief periods during summer and minimize respiratory carbon losses in cold conditions.

南极冰封大陆的陆地植物区系仅分布于零星分布的无冰区域，且以地衣（lichens）和苔藓植物（bryophytes）为优势类群。这些植物常年面临零下低温、强风以及水分匮乏的胁迫，所有这些环境因子均会影响其存活与生长能力。
但南极苔藓的冠层温度可显著高于空气温度。正午时分，冠层温度可超过15℃，具体数值取决于苔藓垫的含水量。
本研究针对6种南极苔藓物种测定了光合最适温度，这些物种采自乔治王岛（maritime Antarctica）以及/或者东南极的风车群岛（Windmill Islands），具体包括：Bryum pseudotriquetrum、Ceratodon purpureus、Chorisodontium aciphyllum、Polytrichastrum alpinum、Sanionia uncinata 及 Schistidium antarctici。
叶绿素荧光（chlorophyll fluorescence）与气体交换（gas exchange）测定结果均显示，电子传递速率（electron transport rate）的最大值出现在冠层温度高于20℃的条件下。
对于3种东南极苔藓物种，其CO₂净同化（net assimilation of CO₂）与光保护热耗散（photoprotective heat dissipation）的最适温度均为20~30℃；当温度低于10℃时，叶肉导度（mesophyll conductance）与0无显著差异。
线粒体呼吸速率的最大值出现在温度高于35℃的条件下，而在5℃时，呼吸速率约降低80%。
尽管南极苔藓在冬季面临极端低温环境，但其光合机构（photosynthetic apparatus）似乎更适应温暖的温度条件。
我们对总碳平衡的估算结果显示，南极苔藓在这类寒冷环境中的存活，可能依赖于在夏季短暂时段内最大化光合效率、并在低温条件下最小化呼吸碳损耗的能力。