Tropical conifer response to altered CO₂ concentration

Conifers dominated the lowland tropics 100 million years ago, but have now been largely replaced by angiosperms, coincident with a large decline in atmospheric CO₂. Using greenhouse treatments of pre-industrial (280 ppm), ambient (400 ppm) and Eocene (800 ppm) CO₂ levels, Dalling et al. demonstrate that seedlings of tropical conifers show stronger growth enhancement with increasing CO₂ than angiosperms.

The conifers also exhibit greater water-use efficiency (WUE), reflecting both increased photosynthetic rate and reduced stomatal conductance under elevated CO₂. High plasticity in photosynthetic and WUE traits may help account for the continued persistence of conifers despite dramatic changes in CO₂ levels since the Eocene epoch.