Physiological characteristics of land plants in relation to environment through time

Abstract

ABSTRACTThe spatially fixed sporophyte body of vascular land plants has to be adapted to both atmospheric and substrate environments. Potentially almost all stages in the life cycle of a land plant are fossilisable and the physiological adaptations to these environments are reflected in the morphology, anatomy, and chemistry of the plant. Although solutions to the plant's physiological problems have been refined through evolution, the basic responses to fundamental environmental parameters such as temperature, water availability, nutrient supply, gas exchange and light, evolved early in land plant history. These taxon-independent solutions can be used qualitatively, and sometimes quantitatively, to track changes in atmospheric and edaphic conditions throughout much of the Phanerozoic. Increase in body size and height in Middle and Late Devonian times was coupled with intense demand for light, nutrients and water supply and with elaborations of vascular systems, photosynthetic surfaces, organ abscission and ‘root’ organisation. During the Carboniferous extreme adaptations to substrate waterlogging evolved. Mycorrhizal associations and “phi” layers in Triassic roots represent early aspects of modern root physiology. From the mid-Cretaceous, angiosperms exhibit leaf architectural characteristics which in modern plants relate qualitatively to moisture and light, and quantitatively to temperature, while vessel size and distribution in trunk wood is related to water stress and susceptibility to freezing. The relative proportion of plants utilising C3, CAM, and C4photosynthetic pathways varies with environment. Isotopic analysis of plant fossils may demonstrate changing relative frequencies of photosynthetic pathways through time in relation to atmospheric composition and temperature.