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Palaeo Leaf Economics Reveal a Shift in Ecosystem Function Associated with the End-Triassic Mass Extinction Event

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Palaeo Leaf Economics Reveal a Shift in Ecosystem Function Associated with the End-Triassic Mass Extinction Event See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/318473239 Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event Article in Nature Plants · July 2017 DOI: 10.1038/nplants.2017.104 CITATIONS READS 7 428 7 authors, including: Wuu Kuang Soh Karen Bacon University College Dublin University of Leeds 14 PUBLICATIONS 79 CITATIONS 15 PUBLICATIONS 167 CITATIONS SEE PROFILE SEE PROFILE Margret Steinthorsdottir Andrew C Parnell Swedish Museum of Natural History Maynooth University 30 PUBLICATIONS 408 CITATIONS 103 PUBLICATIONS 5,129 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Mid-Cretaceous south polar forests View project Response of pan-Arctic permafrost peatlands to rapid climate warming View project All content following this page was uploaded by Wuu Kuang Soh on 24 March 2019. The user has requested enhancement of the downloaded file. ARTICLES PUBLISHED: XX XX 2017 | VOLUME: 3 | ARTICLE NUMBER: 17104 Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event W. K. Soh1*,I.J.Wright2,K.L.Bacon3, T. I. Lenz2, M. Steinthorsdottir4,5,A.C.Parnell6 and J. C. McElwain1 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 paleoecological strategy of fossil plant taxa. We show that paleo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness (CT) observed among extant gymnosperms. Application of this new paleo-LMA proxy to fossil gymnosperms from east Greenland reveals significant shifts in the dominant ecological strategies of vegetation found across the Triassic–Jurassic (Tr–J) 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. he functioning of modern terrestrial ecosystems is determined and the mean global temperature increased by up to 4 °C7. Our largely by the ecological strategies of dominant plant taxa as study taxa, Ginkgoales and Bennettitales (an extinct group of ‘seed Tthese influence the rate at which elements and energy are ferns’), showed contrasting ecological fates: the former predominated moved through the whole system1. Theoretical, experimental and in the post-Tr–J warming interval following near extirpation in east modelling studies have all forecasted that rising CO2 will alter the Greenland, and the latter were common in the Late Triassic but ecological composition of future plant communities2,3 but the direc- underwent sharp ecological decline across the Tr–J transition, and tion and functional implications of these changes in the long-term eventually becoming locally extinct in the post-warming interval12. remain unclear. One promising way forward is to study how ecosys- LMA is a key trait in the measurement and categorization of tem properties changed in response to analogous climate change: plant ecological strategies19,20. It represents the dry mass and nutri- global warming events in the deep past. Here we investigate ent construction costs per unit leaf area, and is tightly correlated 4–6 SUPPLEMENTARY7 INFORMATION whether increased atmospheric CO2 and global warming resulted with many important functional attributes of a leaf including its life- in a shift in ecosystem-scale ecological strategy and function across span, nitrogen concentration,VOLUME: maximum 3 | ARTICLE potential NUMBER:2017.104 photosynthetic the Tr–J boundary (201.36 ± 0.17 million years ago (Ma)8). To do rate and defence chemistry21,22. ARTICLES thisIn the we format estimated provided the LMA by ofthe 109 authors fossil taxaand fromunedited. Astartekløft in PUBLISHED: XX XX 2017 | VOLUME: 3 | ARTICLE NUMBER: 17104 east Greenland (Bennettitales and Ginkgoales) across the Tr–J tran- Results sition9–11, and analysed these data together with information on Paleo-LMA proxy development. To investigate ecological change changes in the relative abundance of these taxa12 and other paleoeco- across the Astartekløft Tr–J transition, we developed a paleo-LMA logical and climatological data4,11,13,14. The Astartekløft locality pro- proxy by quantifying a tight linear scaling relationship between Palaeo leaf economics reveal a shift in ecosystemfl vides evidence for an extreme CO2-induced global warming event, an cuticle thickness and LMA among 20 species of extant at-leaved abrupt decline in plant diversity, regional turnover of dominant taxa gymnosperms (Fig. 1a). The positive relationship between LMA and functionand ultimately to alteration associated in species composition and with vegetation theleaf lifespan end-Triassic underpins a leaf economic spectrum mass that runs from structure5,12,15. Palynological evidence has shown that the floral turn- slow-return species with high LMA, long leaf lifespans, low nutrient over at Astartekløft coincides with the end-Triassic marine mass concentrations and slow physiological rates, to low-LMA fast-return extinction event (ETE) in St Audrie event’s Bay, UK10 and was broadly con- species with short leaf lifespans and high nutrient concentrations temporaneous with a major decline in conifers and woody taxa in and physiological rates21–23. Similarly, the leaf cuticle has many 9,16 W.other K. global Soh localities1 ,I.J.Wright. A rapid2,K.L.Bacon doubling of atmospheric3, T. I. Lenz carbon2, M.intrinsically Steinthorsdottir linked functions4,5,A.C.Parnell of ecological6 significance such as dioxide to around* 2,000–2,500 ppm4 (Supplementary Fig. 1) was defence, protection against harsh environments, water repellence 1 17,18 24 accompaniedand J. C. McElwain by emissions of SO2 and other volcanic gases , and mechanical support . Ultimately, the cuticle protects the costly Climate1School of Biologychange and is Environmental likely to have Science, altered Earth the Institute, ecological University functioning College Dublin, of Bel pastfield, ecosystems, Dublin 4, Ireland. and2Department is likely toof Biological alter functioning Sciences, in theMacquarie future; University, however, Sydney, the New magnitude South Wales and 2109, direction Australia. of3School such of changes Geography, are University difficult of Leeds, to predict. Leeds LS2 Here 9JT, we UK. use4Department a deep-time of Geological case Sciences and Bolin Centre for Climate Research, Stockholm University, SE 109 61 Stockholm, Sweden. 5Department of Paleobiology, Swedish Museum of study to evaluate the impact of a well-constrained CO2-induced global warming event on the ecological functioning of dominantNatural History, plant SE-104 communities. 05 Stockholm, We Sweden. use6 leafSchool mass of Mathematics per area & (LMA), Statistics, a Insight widely Centre used for trait Data inAnalytics, modern University plant Collegeecology, Dublin, to infer Belfield, the paleoecologicalDublin, Ireland. *e-mail: [email protected] of fossil plant taxa. We show that paleo-LMA can be inferred from fossil leaf cuticles based on a tight relationship between LMA and cuticle thickness (CT) observed among extant gymnosperms. Application of this new paleo-LMANATURE PLANTS proxy3, 17104 (2017) to fossil | DOI: 10.1038/nplants.2017.104 gymnosperms from| www.nature.com/natureplants east Greenland reveals significant shifts in the dominant ecological1 strategies of vegetation found across the Triassic–Jurassic (Tr–J) 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. he functioning of modern terrestrial ecosystems is determined and the mean global temperature increased by up to 4 °C7. Our largely by the ecological strategies of dominant plant taxa as study taxa, Ginkgoales and Bennettitales (an extinct group of ‘seed Tthese influence the rate at which elements and energy are ferns’), showed contrasting ecological fates: the former predominated moved through the whole system1. Theoretical, experimental and in the post-Tr–J warming interval following near extirpation in east modelling studies have all forecasted that rising CO2 will alter the Greenland, and the latter were common in the Late Triassic but ecological composition of future plant communities2,3 but the direc- underwent sharp ecological decline across the Tr–J transition, and tion and functional implications of these changes in the
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