Preprints
https://doi.org/10.5194/bg-2021-139
https://doi.org/10.5194/bg-2021-139

  04 Jun 2021

04 Jun 2021

Review status: this preprint is currently under review for the journal BG.

The Cretaceous physiological adaptation of angiosperms to a declining pCO2: a trait-oriented modelling approach

Julia Bres, Pierre Sepulchre, Nicolas Viovy, and Nicolas Vuichard Julia Bres et al.
  • Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France

Abstract. The Cretaceous evolution of angiosperm leaves towards higher vein densities enables unprecedented leaf stomatal conductance. Still, simulating and quantifying the impact of such change on plant productivity and transpiration in the peculiar environmental conditions of the Cretaceous remains challenging. Here, we address this issue by combining a paleo proxy-based model with a fully atmosphere-vegetation model that couples stomatal conductance to carbon assimilation. Based on the fossil record, we build and evaluate three consistent pre-angiosperm vegetation parameterizations under two end-members scenarios of pCO2 (280 ppm and 1120 ppm) for the mid-Cretaceous : a reduction of hydraulic or photosynthetic capacity and a combination of both, supported by a likely coevolution of stomatal conductance and photosynthetic biochemistry. Our results suggest that decreasing hydraulic or/and photosynthetic capacities always generates a reduction of transpiration that is predominantly the result of plant productivity variations, modulated by light, water availability in the soil and atmospheric evaporative demand. The high pCO2 acts as a fertilizer on plant productivity that bolsters plant transpiration and water-use efficiency. However, we show that pre-angiosperm physiology does not allow vegetation to grow under low pCO2 because of a positive feedback between leaf stomatal conductance and leaf area index. Our modelling approach stresses the need to better represent paleovegetation physiological traits. It also confirms the hypothesis of a likely evolution of angiosperms from a stage of low hydraulic and photosynthetic capacities at high pCO2 to a stage of high hydraulic and photosynthetic capacities linked to leaves more and more densely irrigated together with a more efficient biochemistry at low pCO2.

Julia Bres et al.

Status: open (until 17 Jul 2021)

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Julia Bres et al.

Julia Bres et al.

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Short summary
The purpose of this paper is to (1) to implement angiosperm paleo-traits in a land-surface model according to the fossil record, (2) assess this paleo-vegetation functioning under different pCO2. We show that photosynthesis, transpiration and water-use efficiency are dependent on both the vegetation parameterization and the pCO2. Comparing the modeled vegetation with the fossil record, we provide clues on how to account for angiosperm evolutionary traits in paleoclimate simulations.
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