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.

中文翻译：

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白垩纪被子植物对 pCO ₂下降的生理适应：一种以性状为导向的建模方法

摘要。被子植物的白垩纪叶向更高的静脉密度进化，使叶气孔导度达到前所未有的水平。尽管如此，模拟和量化这种变化对白垩纪特殊环境条件下植物生产力和蒸腾作用的影响仍然具有挑战性。在这里，我们通过将基于古代理的模型与将气孔导度与碳同化相结合的完全大气植被模型相结合来解决这个问题。基于化石记录，我们在 pCO _{2 的}两个终端成员情景下构建和评估了三个一致的前被子植物植被参数化（280 ppm 和 1120 ppm）对于白垩纪中期：水力或光合能力的降低以及两者的结合，由气孔导度和光合生物化学的可能共同进化支持。我们的结果表明，水力或/和光合能力的降低总是会导致蒸腾作用的减少，这主要是植物生产力变化的结果，受光照、土壤中的水分可用性和大气蒸发需求的调节。高 pCO ₂作为植物生产力的肥料，可提高植物蒸腾作用和水分利用效率。然而，我们表明前被子植物生理学不允许植被在低 pCO ₂下生长因为叶气孔导度和叶面积指数之间存在正反馈。我们的建模方法强调需要更好地代表古植被生理特征。它还证实了被子植物可能从高 pCO ₂下的低水力和光合能力阶段进化到高水力和光合能力的阶段的假设，这与叶片越来越密集的灌溉以及低 pCO 下更有效的生物化学有关₂ .