Stomata Density of Orchids and Cloud Forest Humidity in Monteverde, Costa Rica

This experiment explored stomata densities of the epiphytic Pleurothallis aristata and Maxillaria sp. orchids under experimental conditions of dry and humid environments. Pleurothallis aristata is in the sub-tribe Pleurothallidinae and lacks pseudobulbs, while Maxillaria sp. has pseudobulbs. The purpose of the experiment was to test if there was a difference in stomata densities between the two species, and if there was a difference in mean percent stomata open in humid and dry environments. Stomata impressions were taken from the leaves of twenty individuals of each species using clear nail polish peels that were examined under a compound microscope. The results show that there is a significant difference in stomata density between the Pleurothallis aristata and the Maxillaria sp. (Rank Sum Test, t=55, n1=10, n2=10, p<0.05). The results also show that both species had a higher percentage of open stomata in humid environments than in dry environments (Wilcoxon sign rank test). An explanation for these results is that Maxillaria sp. has a pseudobulb for water storage, has a larger leaf surface area, and therefore has higher stomata density. Both species would also close their stomata in drier conditions in order to reduce water loss and desiccation. This research is significant because it relates to problems such as climate change and shifting of biomes, as some species may be more likely to succeed in periods of prolonged drought or less humidity.