Epiphytic bromeliads in a changing world: the effect of elevated CO2 and varying water supply on growth and nutrient relations

Global climate change is likely to impact all plant life. Vascular epiphytes represent a life form that may be affected more than any other by possible changes in precipitation leading to water shortage, but negative effects of drought may be mitigated through increasing levels of atmospheric CO2. We studied the response of three epiphytic Aechmea species to different CO2 and watering levels in a full-factorial climate chamber study over 100days. All species use crassulacean acid metabolism (CAM). Response variables were relative growth rate (RGR), nocturnal acidification and foliar nutrient levels (N, P, K, Mg). Both elevated CO2 and increased water supply stimulated RGR, but the interaction of the two factors was not significant. Nocturnal acidification was not affected by these factors, indicating that the increase in growth in these CAM species was due to higher assimilation in the light. Mass-based foliar nutrient contents were consistently lower under elevated CO2, but most differences disappeared when expressed on an area basis. Compared to previous studies with epiphytes, in which doubling of CO2 increased RGR, on average, by only 14%, these Aechmea species showed a relatively strong growth stimulation of up to +61%. Consistent with earlier findings with other bromeliads, elevated CO2 did not mitigate the effect of water shortage.