Original paper
Leaf traits of long-ranging Paleogene species and their relationship with depositional facies, climate and atmospheric CO2 level
Moraweck, Karolin; Grein, Michaela; Konrad, Wilfried; Kvaček, Jiří; Kova-Eder, Johanna; Neinhuis, Christoph; Traiser, Christopher; Kunzmann, Lutz
Palaeontographica Abteilung B Volume 298 Issue 4-6 (2019), p. 93 - 172
227 references
published: Jun 27, 2019
Abstract
Leaves are the most appropriate plant organs for studying adaptations to environmental changes as they are the locations of photosynthetic metabolism and thus directly exposed to habitat conditions. Besides investigations on complete assemblages, individual long-ranging species could directly mirror adaptations and changes of leaf traits on environmental, climate and atmospheric CO2 level evolution over a considerable time span. Central European leaf assemblages from the middle and late Paleogene reveal plenty of properly preserved fossils that are quite suitable and promising for investigating functional leaf traits of woody dicots. Herein, morphological, morphometric and micromorphological (cuticular) functional leaf traits, both quantitative and qualitative parameters, of Rhodomyrtophyllum reticulosum (Myrtaceae) and Platanus neptuni (Platanaceae) are analysed. The aim is to evaluate whether leaf traits of both taxa reflect environmental conditions including climate and if leaf traits track local, regional and/or global trends of palaeoclimate and palaeo-atmospheric CO2 evolution. Both species cover a time span from the early-middle Eocene boundary to the earliest Miocene, appr. 26 Ma, with an overlap in their occurrences in the late Eocene. Altogether material of 23 sites from 3 distinct depositional palaeoenvironments, i. e. marine, coastal lowland/alluvial plain and volcanic settings, is considered. Basic information on regional palaeoclimate parameters were calculated from the fossil plant assemblages using the Coexistence Approach and the Climate Leaf Analysis Multivariate Program (CLAMP). The results indicate high variability of morphological and morphometric leaf traits within the sites for Rhodomyrtophyllum reticulosum but almost no substancial changes between sites of the middle-late Eocene stratigraphic sequence. Platanus neptuni leaf trait changes, macromorphological as well as micromorphological data, correspond to differences in depositional settings and habitat. Stomatal density, trichome density and stomata size of Platanus neptuni vary in time and depend on the respective depositional setting. Palaeo-atmospheric CO2 levels are reconstructed for seven Eocene and seven Oligocene sites by gas exchange modelling using several leaf traits of the fossil-species as well as of their extant relatives. Results reveal similar mean CO2 concentrations of 397 to 656 ppm for the Eocene using Rhodomyrtophyllum reticulosum data; extant input data are based on Syzygium samarangense. Data provided by Platanus neptuni, based on extant Platanus kerrii, indicate quite stable CO2 values during the Oligocene with mean concentrations of 393 to 565 ppm. Results are comprehensively discussed with respect to various influences of methodological constrains, taphonomic filters, and depositional settings. The interpretation of the data leads to the conclusion that leaf traits of both long-ranging fossil-species are valuable proxies for tracing environmental evolution but their ecophysiological signals in response to global changes are less pronounced and affected by habitat characteristics.
Keywords
Fossil leaves • Platanus neptuni • Rhodomyrtophyllum reticulosum • stomatal density • trichome density • morphometric traits • leaf mass per area • gas exchange modelling