Growth of epiphytic bromeliads in a changing world: The effects of CO2, water and nutrient supply

Vascular epiphytes, which respond to varying water supply more than any other life form, are thought to be particularly vulnerable to climate change because they are de-coupled from the soil and are thus more directly affected by atmospheric conditions. The few available studies addressing the effect of climate change on epiphytes have either studied plant responses to changes in water supply or to elevated CO2, but none has looked at possible interactions of these abiotic factors. Here, we present a growth chamber study on the response of individuals of 11 species of epiphytic bromeliads from both tropical lowlands and montane areas to varying CO2, water and nutrient levels. Water availability had by far the strongest and most consistent impact on plant growth, while the effects of elevated CO2 and increased nutrient supply were much less consistent across species or habitats. A significant mitigation of reduced water availability by increased CO2 levels could not be detected. While some species from montane areas were very susceptible to low water availability, lowland species were mostly quite drought-tolerant. These results suggest that global change can pose a real threat to vascular epiphytes through changes in the altitude of cloud formation and altered precipitation patterns, acknowledging substantial differences between species and habitats. Other aspects of global change like the increase of atmospheric CO2 levels as such seem of limited relevance for the functioning of epiphytic plants.