Gas exchange in Ranunculus species and the evolution of alpine herbaceous plant physiology

Abstract

Buttercup species (Ranunculus) in the Australian Alps vary in their leaf morphology and soil moisture preference, but little is known about their rates of gas exchange. Gas exchange rates of three buttercup species, R. graniticola, R. muelleri and R. dissectifolius, were measured under three conditions (ambient CO₂, unlimited CO₂ (to test maximum photosynthetic rate) and decreased water vapour (to test rates under water stress)) using an infrared gas analyser. There was no statistically significant variation in gas exchange rates between any of the species for any of the conditions. This then begs the question of why morphology has undergone such clear divergent evolution while physiology has not. This paper argues that every morphological ‘decision’ a plant makes has trade-offs and the result of this is the existence of many optimal morphologies that are advantageous in different ways. However, because physiology can change instantaneously to optimise plant growth in different environmental conditions, it does not face the same sort of trade-offs and thereby, plants have fewer options for diverse advantageous physiologies.