Do CO2, temperature, rainfall and elevation influence stomatal traits and leaf width in Melaleuca lanceolata across southern Australia?

Abstract

Herbarium specimens and contemporary collections were used to investigate the effects of environment and CO2 concentration on stomatal density, stomatal size, maximum potential water loss through stomata (gwmax) and leaf width of Melaleuca lanceolata Otto in southern Australia. Variation in CO2 had no effect on stomatal size and density, or gwmax of M. lanceolata. In contrast, stomatal density was negatively correlated with annual rainfall and there were significant, positive relationships between both elevation and mean maximum temperature and stomatal density. There was also a positive relationship between gwmax and maximum temperature. Leaf width was negatively correlated with both maximum temperature and elevation. We suggest that the increase in stomatal density and gwmax with increasing maximum temperatures enhances the potential for evaporative cooling of M. lanceolata leaves. It could also allow plants to maximise opportunities for carbon fixation during the sporadic rainfall events that are typical of drier, northern regions. This occurs in conjunction with a narrowing of the leaves in warmer climates and higher elevations, which results in a decrease in the thickness of the boundary layer. This combination of smaller leaves and increased potential for evaporative cooling through increased stomatal density and gwmax would allow the leaf to stay closer to its optimal temperature for photosynthesis.