Effect of enriched CO2 atmosphere on morphological and chemical characteristics of Alternanthera philoxeroides

Abstract

Carbon dioxide (CO2) is one of the vital resources for plants and its concentrations in the atmosphere have been on the increase globally from the 18th century, and continue to rise at approximately 0.4% per year. Atmospheric CO2 enrichment could possibly modify growth and chemical profiles of plants, as well as plant–insect interactions. The present study investigated the effects of elevated atmospheric CO2 on stem diameters, above-ground biomass and secondary metabolite components of both terrestrial and aquatic forms of Alternanthera philoxeroides. Stem fragments of the weed were grown in six Open Top Chambers (OTCs): three chambers of ambient (~400 ppm) and three chambers of elevated (~1000 ppm) CO2 levels to simulate the current and future CO2 levels, respectively, based on prediction by IPCC (2013). Total dry weights of leaves and stems, as well as stem diameters were measured to evaluate growth and biomass accumulation in A. philoxeroides. Furthermore, chemical analyses were performed on leaf tissues of plants grown under both elevated and ambient atmospheric CO2 treatments to determine the concentration of secondary metabolites (phenolic acids and flavonoids). Results of the analyses revealed that CO2 enrichment significantly increased stem diameters and enhanced above-ground biomass accumulation in both aquatic and terrestrial environments. Enriched CO2 atmosphere treatments increased concentration of secondary metabolites in leaf tissues, with leaves of plants grown under elevated CO2 exhibiting remarkably higher concentrations of phenolic acids and flavonoids. Total flavonoid content increased by 51.02% in aquatic plants and by 99.03% in terrestrial plants. Total phenolic content increased by 29.57% in aquatic plant leaves while in terrestrial plant leaves the increase was by 61.11%. Above-ground biomass accumulation and increase in stem diameters could enhance competitive ability of the species and its ability to invade and colonize new habitats in response to a future CO2-enriched atmosphere.