Inselbergs are terrestrial pre-Cambrian rocky islands within forest and savanna formation. Within this rock outcrops is common to find sub-islands of small plant communities growing in cracks and cavities in the rock, exposed to elevated temperatures (up to 55ºC), high radiation and limited access to water and nutrients because of the shallow soils. As result of the harsh edaphic and microclimatic conditions typical of the Inselbergs and their island-type nature, they are extremely rich in endemic species adapted to deal with all these stresses together. However, difficult access to these ecosystems has hindered the study in situ of the ecophysiological mechanisms that allow plants to thrive in one of the harshest environment on earth. In this study, we measured a series of functional traits related to leaf structure, stomata characteristics, plant water status, leaf-level gas exchange and chlorophyll a fluorescence in three of the most common vascular plant species found in the Inselbergs from Vichada near the Orinoco river in Colombia: Acanthella sprucei, Mandevilla caurensis, Tabebuia orinocensis. All measurements were taken at the end of the wet season and beginning of the dry season in 2017.
Results/Conclusions
We could distinguish two physiological strategies in our three studied species. One in A. sprucei who had the highest number of stomata per area (115 st/μm2), the highest stomatal conductance (0.60 mH2O/m2/s), and lowest water use efficiency (WUE), all traits that related with its better temperature regulation ability and relatively higher CO2 uptake(17 μmCO2/m2/s). The second strategy found in M. caurensis and T. orinocensis is to have a lower number of stomata per area and lower stomatal conductance but higher WUE. However, the two species differed in their maximum CO2 assimilation (Amax), where T. orinocensis had the lowest value found in all three species (8 μmCO2/m2/s) and M. caurensis the highest Amax (26 μmCO2/m2/s). Fluorescence measurements (Fv/Fm) taken at predawn and midday indicates that all species started the day with no signs of stress but at noon Fv/Fm decreased suggesting that at noon all species were stressed and unable to process all the light energy they were receiving. However,Fv/Fm values of the most stressed plant were never lower than 0.70, suggesting that all species in this habitat are able to deal with high irradiance inputs with little photodamage. Our data show that different species use different physiological mechanisms to thrive in the Inselbergs extreme conditions.