The Impact of Angiosperms Physiological Evolution on Earth Systems

The physiological evolution of vegetation affects the interaction between vegetation and climate. Angiosperms have higher leaf vein density than all other plants throughout evolutionary history, contributing to higher transpiration capacities. However, the climatic response to changes in physiological functions of angiosperms has remained to be determined. Here, Community Earth System Model (CESM) version 1.2.2 and BIOME4 vegetation model are applied to simulate the world without angiosperms by reducing the maximum carboxylation rate (Vmax) to 1/4 (Boyce et al, 2009), in conditions of both fixed and non-fixed vegetation distribution. First, we maintain the pre-industrial vegetation distribution, the results illustrate that the world without angiosperms would have less productivity, higher global mean temperature, consisting with the results of Boyce and Lee (Boyce and Lee, 2010). In addition, the warmer southern hemisphere and colder northern hemisphere are identified, which are caused by the decrease of the strength of Atlantic Meridional Overturning Circulation (AMOC). Second, we consider changes of vegetation structure, the results show that temperature and precipitation would vary significantly locally, and the area of tropical forest would decline sharply in the world without angiosperms, which may affect biodiversity. The evolution of physiological functions of angiosperms influences climate and provides potential competitive advantages for angiosperms to dominate modern vegetation.