During the early Tertiary, the genus Metasequoia was widely distributed and abundant in the high Arctic, suggestive of an adaptive fit between the Arctic paleoenvironment and the physiology of this relic genus. While present day temperature is clearly restrictive for growth in the Arctic, evidence suggests that the paleotemperature was much more benign. In contrast, the light regime can be assumed unchanged, with annual periods of several months of continuous light and continuous darkness at the high latitudes influencing the plants that populated its paleolandscape. Previously, we have shown that the continuous-light environment is stressful for plant photosynthesis and related metabolic pathways. Here we explore the photosynthetic response along with carbon and nutrient allocation of Metasequoia glyptostroboides, Taxodium distichum and Sequoia sempervirens when exposed to a continuous-light treatment. Our findings indicate that Metasequoia has the unique combination of indeterminate growth and deciduous habit that may have been the key adaptations for the paleoarctic. Taxodium, a deciduous species with indeterminate growth, fails to develop a strong carbon sink and, therefore, suffers from photosynthetic inhibition by end-product accumulation. The absence of Sequoia (a close relative of Metasequoia) in the paleoarctic can best be attributed to its nondeciduous habit, possibly compounded by calcium or other nutrient deficiencies.
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