Isoprene emission and primary metabolism in Phragmites australis grown under different phosphorus levels.

Aquatic plants are generally used for wastewater purification and phytoremediation,but some of them also emit large amounts of isoprene, themost abundant biogenic volatile organic compound. Since isoprenoid biosynthesisrequires high amounts of phosphorylated intermediates, the emissionmay also be controlled by inorganic phosphorus concentration (Pi) inleaves. We carried out experiments to determine the emission of isoprenefrom Phragmites australis plants used in reconstructed wetlands to phytoremediateelevated levels of phosphorus contributed by urban wastes. Fourgroups of plants were grown hydroponically in water containing differentlevels of KH2PO4. High levels of phosphorus in the water resulted in highPi in the leaves. High Pi stimulated photosynthesis at intercellular CO2concentrations lower and higher than ambient, implying higher ribulose1,5-bisphosphate carboxylase (Rubisco) activity and higher ribulose 1,5-bisphosphateregeneration rates, respectively. However, isoprene emission wassubstantially lower at high Pi than at low Pi, and was not associated to photosynthesisrates at high Pi. This surprising result suggests that isoprene islimited by processes other than photosynthetic intermediate availability orby energetic (ATP) requirements under high Pi levels. Irrespective of themechanism responsible for the observed reduction of isoprene emission, ourresults show that Phragmites plants may effectively remove phosphorus fromwater without concurrently increase isoprene emission, at least on a leafarea basis. Thus, Phragmites used in reconstructed wetlands for phytoremediationof urban wastes rich of phosphates will not contribute high loads ofhydrocarbons which may influence air quality over urban and peri-urbanareas.