Relationship between stomatal density, size and speed of opening in Sumatran rainforest species.

Recent studies have suggested that an association between size and speed of stomatal opening of stomata within taxa is likely to play a role in photosynthesis and transpiration. In this study we investigate whether this correlation applies for seedlings of 11 rainforest species from different taxa, and whether differences in stomatal and gas exchange parameters were related to initial growth under field and controlled conditions. The experiment was conducted on seedlings of nine late successional species and two early successional species, placed in full sunlight or 70% shade. We assessed density, size, length and width of guard cells, coupled with gas exchange parameters in the transition from darkness to light, recording minimum stomatal conductance during daytime darkness (gs-dark), operating maximum stomatal conductance (gs-op), speed of stomatal opening and the time to reach 50% conductance (T-50%). All stomata and gas exchange parameters were different between species. Shade significantly affected size and density, and all gas exchange parameters except gs-op were different between light situations. Stomatal size correlated negatively with speed of opening and positively with T-50%, confirming that smaller stomata open faster than large stomata. The two early successional species were very different in stomatal size and density, and in response to light. Anatomic parameters and physiological traits were not related to height growth, but gs-dark, gs-op and speed of stomatal opening were associated with biomass growth in a subselection of six late successional species.