Physiological Ecology of Metasequoia glyptostroboides Hu et Cheng

Abstract

Morphologically identical representatives of the modem taxon Metasequoia glyptostroboides Hu et Cheng have been found as fossils in many Northern Hemisphere locations, indicating that since its origin in the Late Cretaceous, the genus has migrated throughout the Northern Hemisphere, and at times had a range extending over some 40 degrees of latitude. Today, the taxon is found only in a restricted area in southern China; however, it has been disseminated widely as a horticultural curiosity, and grows successfully in a variety of modem habitats. This paper examines the modem species' autecology, focusing on gas exchange relations, to address the role of physiological constraints in range contraction over time. Examination of CO, uptake and transpiration in response to light, temperature, humidity and CO, concentration indicate that M. glyptostroboides is drought-intolerant, adapted to low light levels and relatively cool climates, as might be expected in foggy coastal or riparian habitats. The gas-exchange relations of the modem species are sufficiently flexible to explain the presence of fossil Metasequoia Miki at all known sites, based on paleoclimatic reconstructions, implying that the species has not undergone any major adaptive changes in its core physiological processes. In spite of its horticultural popularity, there has been relatively little quantitative physiological examination of this species. This paper attempts to summarize what is available in the literature, providing an additional perspective on the species autecology in the context of species migration and habitat selection. Metasequoia glyptostroboides is shade-intolerant, germinates best on open soils, intolerant of high light levels and resists pests and disease well due to the accumulation of toxic secondary compounds. Finally, the role of M. glyptostroboides' deciduous habit is discussed with reference to adaptation to high-latitude photoseasonality.