Margret Steinthorsdottir

Deep-time evidence of a link between elevated CO2 concentrations and perturbations in the hydrological cycle via drop in plant transpiration

The physiological effects of high CO 2 concentrations, i.e., [CO 2 ], on plant stomatal responses may be of major importance in understanding the consequences of climate change, by causing increases in runoff through suppression of plant transpiration. Radiative forcing by high [CO 2 ] has been the main consideration in models of global change to the exclusion of plant physiological forcing, but this potentially underestimates the effects on the hydrological cycle, and the consequences for ecosystems. We tested the physiological responses of fossil plants from the Triassic–Jurassic boundary transition (Tr–J) succession of East Greenland. This interval marks a major high CO 2 -driven environmental upheaval, with faunal mass extinctions and significant floral turnover. Our results show that both stomatal size (expressed in fossil material as SL, the length of the stomatal complex opening) and stomatal density (SD, the number of stomata per mm 2 ) decreased significantly during the Tr–J. We estimate, using a leaf gas-exchange model, that the decreases in SD and SL resulted in a 50%–60% drop in stomatal and canopy transpiration at the Tr–J. We also present new field evidence indicating simultaneous increases in runoff and erosion rates. We propose that the consequences of stomatal responses to elevated [CO 2 ] may lead to locally increased runoff and erosion, and may link terrestrial and marine biodiversity loss via the hydrological cycle.

Paleoecology, Ploidy, Paleoatmospheric Composition, and Developmental Biology: A Review of the Multiple Uses of Fossil Stomata

Fossil plant stomata reveal insights into the evolution of atmospheric composition, trends in plant genome size, and the biology of the living plant prior to fossilization.

Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event

Climate change is likely to have altered the ecological functioning of past ecosystems, and is likely to alter functioning in the future; however, the magnitude and direction of such changes are difficult to predict. Here we use a deep-time case study to evaluate the impact of a well-constrained CO2-induced global warming event on the ecological functioning of dominant plant communities. We use leaf mass per area (LMA), a widely used trait in modern plant ecology, to infer the palaeoecological strategy of fossil plant taxa. We show that palaeo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness observed among extant gymnosperms. Application of this new palaeo-LMA proxy to fossil gymnosperms from East Greenland reveals significant shifts in the dominant ecological strategies of vegetation found across the Triassic–Jurassic transition. Late Triassic forests, dominated by low-LMA taxa with inferred high transpiration rates and short leaf lifespans, were replaced in the Early Jurassic by forests dominated by high-LMA taxa that were likely to have slower metabolic rates. We suggest that extreme CO2-induced global warming selected for taxa with high LMA associated with a stress-tolerant strategy and that adaptive plasticity in leaf functional traits such as LMA contributed to post-warming ecological success.

EVIDENCE FOR INSECT AND ANNELID ACTIVITY ACROSS THE TRIASSIC-JURASSIC TRANSITION OF EAST GREENLAND

Abstract During a study of macroflora from the Astartekløft locality in Jameson Land, East Greenland, endophytic insect ovipositions (egg traces) belonging to ichnogenus Paleoovoidus were recorded for the first time in ginkgoalean (Ginkgoites, Sphenobaiera, and Baiera) fossil leaves across the Triassic–Jurassic (Tr–J) transition (ca. 200 Ma). The ovipositions may have been produced by insects in the order Odonata (dragonflies and damselflies) and are relatively more abundant before than after the Tr–J transition, possibly reflecting changes in plant-insect association. Fossil clitellate annelid (leech) cocoons were also discovered in a macerated sample from a single bed within the Tr–J transition. The cocoons belong to two species: Dictyothylakos pesslerae and Pilothylakos pilosus, extending the range of the latter genus from the Early Cretaceous to the Early Jurassic. This new evidence suggests that the ecosystem and food webs were profoundly affected by the environmental degradation surrounding the end-Triassic event (ETE), which was marked by faunal mass extinctions and floral turnover. Invertebrate ichno- and body fossils may add significantly to paleoenvironmental information provided by plant fossil assemblages, and therefore a protocol for recording evidence of invertebrate activity in paleobotanical research is suggested, including analyzing a standardized number of specimens for fossil traces and bulk maceration for discovery of invertebrate body fossils. More well-designed studies on Mesozoic plant-invertebrate associations are needed and will provide deeper knowledge about the structure and evolution of complex ecosystems.

Corrigendum: Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event

This corrects the article DOI: 10.1038/nplants.2017.104