Institute of Culture and Environment, Alaska Pacific University, 4101 University Drive, Anchorage, AK 99508, USA.
Department of Geography, University of Utah, 332 S 1400 E, Salt Lake City, UT 84112, USA.
FEMS Microbiol Ecol. 2018 Mar 1;94(3). doi: 10.1093/femsec/fiy007.
Red-colored secondary pigments in glacier algae play an adaptive role in melting snow and ice. We advance this hypothesis using a model of color-based absorption of irradiance, an experiment with colored particles in snow, and the natural history of glacier algae. Carotenoids and phenols-astaxanthin in snow-algae and purpurogallin in ice-algae-shield photosynthetic apparatus by absorbing overabundant visible wavelengths, then dissipating the excess radiant energy as heat. This heat melts proximal ice crystals, providing liquid-water in a 0°C environment and freeing up nutrients bound in frozen water. We show that purple-colored particles transfer 87%-89% of solar energy absorbed by black particles. However, red-colored particles transfer nearly as much (85%-87%) by absorbing peak solar wavelengths and reflecting the visible wavelengths most absorbed by nearby ice and snow crystals; this latter process may reduce potential cellular overheating when snow insulates cells. Blue and green particles transfer only 80%-82% of black particle absorption. In the experiment, red-colored particles melted 87% as much snow as black particles, while blue particles melted 77%. Green-colored snow-algae naturally occupy saturated snow where water is non-limiting; red-colored snow-algae occupy drier, water-limited snow. In addition to increasing melt, we suggest that esterified astaxanthin in snow-alga cells increases hydrophobicity to remain surficial.
冰川藻类中的红色次生色素在冰雪融化中发挥了适应性作用。我们通过基于颜色的辐照度吸收模型、雪粒的着色实验以及冰川藻类的自然史来验证这一假说。类胡萝卜素和酚类物质（雪藻中的虾青素和冰藻中的没食子酸）通过吸收过多的可见光来保护光合作用装置，然后将多余的辐射能转化为热能。这种热量会融化附近的冰晶，在 0°C 的环境下提供液态水，并释放出与冻结水结合的营养物质。我们表明，紫色颗粒将黑色颗粒吸收的太阳能中的 87%-89%转移。然而，红色颗粒通过吸收峰值太阳波长并反射附近冰雪晶体最吸收的可见光，也能转移几乎相同数量的太阳能（85%-87%）；当雪使细胞隔热时，这后一过程可能会减少潜在的细胞过热。蓝色和绿色颗粒仅将黑色颗粒吸收的太阳能中的 80%-82%转移。在实验中，红色颗粒使雪融化的量比黑色颗粒多 87%，而蓝色颗粒使雪融化的量为 77%。绿色雪藻自然存在于水分不限制的饱和雪中；红色雪藻则存在于干燥、水分限制的雪中。除了增加融化量，我们还认为，雪藻细胞中的酯化虾青素增加了疏水性以保持在表面。
