InvestigatingDevonian trees as geo‐engineers of past climates: linking palaeosols to palaeobotany and experimental geobiology

Jennifer L Morris,Joe Quirk,Christopher M Berry,Charles H Wellman,Stephen Hillier,Jonathan R Leake,J Andrew Milton,John E A Marshall,William E Stein,David J Beerling,Frank Mannolini

doi:10.1111/pala.12185

Jennifer L Morris, Joe Quirk + Show 9 more

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AbstractWe present the rationale for a cross‐disciplinary investigation addressing the ‘Devonian plant hypothesis’ which proposes that the evolutionary appearance of trees with deep, complex rooting systems represents one of the major biotic feedbacks on geochemical carbon cycling during thePhanerozoic. According to this hypothesis, trees have dramatically enhanced mineral weathering driving an increased flux ofCa2+to the oceans and, ultimately, a 90% decline in atmosphericCO2levels through thePalaeozoic. Furthermore, experimental studies indicate a key role for arbuscular mycorrhizal fungi in soil–plant processes and especially in unlocking the limiting nutrient phosphorus in soil viaCa‐phosphate dissolution mineral weathering. This suggests co‐evolution of roots and symbiotic fungi since theEarlyDevonian could well have triggered positive feedbacks on weathering rates whereby root–fungalPrelease supports higher biomass forested ecosystems. Long‐standing areas of uncertainty in this paradigm include the following: (1) limited fossil record documenting the origin and timeline of the evolution of tree‐sized plants through theDevonian; and (2) the effects of the evolutionary advance of trees and theirin siturooting structures on palaeosol geochemistry. We are addressing these issues by integrating palaeobotanical studies with geochemical and mineralogical analyses of palaeosol sequences at selected sites across easternNorthAmerica with a particular focus on drill cores fromMiddleDevonian forests inGreeneCounty,NewYorkState.

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We present the rationale for a cross-disciplinary investigation addressing the ‘Devonian plant hypothesis’ which proposes that the evolutionary appearance of trees with deep, complex rooting systems represents one of the major biotic feedbacks on geochemical carbon cycling during the Phanerozoic
T H E evolution and geographical spread of trees with deep, complex rooting systems and their role in the development of soils is widely regarded as the ‘Devonian engine’ that drove major changes in global biogeochemical cycles as the planet became increasingly forested
Fossil (Remy et al 1994; Kenrick and Strullu-Derrien 2014; Strullu-Derrien et al 2014) and molecular clock (Simon et al 1993) evidence indicates that the rooting systems of land plants co-evolved and maintained symbiotic arbuscular mycorrhizal (AM) associations that have played an important role in land colonization and phosphorus uptake by most plants since at least the Early Devonian, even before true roots evolved

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We present the rationale for a cross-disciplinary investigation addressing the ‘Devonian plant hypothesis’ which proposes that the evolutionary appearance of trees with deep, complex rooting systems represents one of the major biotic feedbacks on geochemical carbon cycling during the Phanerozoic. This work provides opportunities for relating the in situ occurrence of the rooting structures of trees of different types and statures to palaeosol weathering profiles beneath, characterized by detailed geochemical and mineralogical analyses.

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