Variety of responses of plant phenolic concentration to CO<inf>2</inf> enrichment

A wide range of responses to elevated CO2 was found for leaf total phenolic concentration of one grass species (wheat) growing in a Free-Air CO2 Enrichment (FACE) system and two woody species (orange and pine trees) growing in Open-Top Chambers (OTC). The total phenolic concentration of wheat flag leaves grown at elevated [CO2] was increased for most of the grain- filling stages studied; there was no significant change in phenolic concentration of CO2-enriched orange tree leaves and CO2-enriched pine tree needles had reduced total phenolic concentration. There was an inverse relationship between the increase in leaf total phenolic concentration and increase in biomass of these pine trees. Different rates of increase in growth (carbon sink) produced by different environmental conditions or different resource availabilities apart from CO2 itself must be considered in order to understand the response of carbon-based-secondary-compounds to elevated CO2.