Long-term effects of elevated CO2, nighttime warming and drought on plant secondary metabolites in a temperate heath ecosystem

Background and Aims Plant secondary metabolites play critical roles in plant stress tolerance and adaptation, and are known to be influenced by the environment and climate changes, yet the impacts and interactions of multiple climate change components are poorly understood, particularly under natural conditions. Methods Accumulation of phenolics and emissions of volatile organic compounds (VOCs) were assessed on heather, Calluna vulgaris, an abundant evergreen dwarf shrub in European heathlands, after 6 years of exposure to elevated CO2, summer drought and nighttime warming. Key Results Drought alone had the strongest effects on phenolic concentrations and compositions, with moderate effects of elevated CO2 and temperature. Elevated CO2 exerted the greatest impact on VOC emissions, mainly by increasing monoterpene emissions. The response magnitudes varied among plant tissue types and chemical constituents, and across time. With respect to interactive effects of the studied climate change components, the interaction between drought and elevated CO2 was most apparent. Drought mainly reduced phenolic accumulation and VOC emissions, while elevated CO2 mitigated such effects. Conclusions In natural ecosystems, co-occurring climate factors can exert complex impacts on plant secondary metabolite profiles, which may in turn alter ecosystem processes.