Effect of elevated carbon dioxide concentration on growth, productivity and glyphosate response of parthenium weed (Parthenium hysterophorus L.).
BACKGROUND: The rise in atmospheric CO2 has huge impacts on the biology and management of invasive weed species such as Parthenium hysterophorus. This study evaluated the effect of ambient (400 ppm) and elevated (700 ppm) CO2 concentrations on P. hysterophorus growth, reproductive output and response to glyphosate applied at several doses including the recommended dose (800 g a.e. ha-1). RESULTS: The plants in control treatment (no herbicide) grew taller (41%), produced a larger number of leaves (13%) and flowers (39%), and higher dry biomass (34%) at elevated CO2 as compared to the ambient CO2. Glyphosate caused significant reduction in chlorophyll content of P. hysterophorus plants grown at both CO2 concentrations in a dose-dependent manner. The percentage herbicide injury was relatively less at elevated CO2 as compared to the ambient CO2 at 7 and 14 days after glyphosate application but it was almost similar at 21 days after application. This shows that elevated CO2 might have slowed the translocation of glyphosate initially, but most plants were killed eventually close to 21 days after application. The survival rate was higher under elevated as compared to the ambient CO2 at recommended and lower doses of glyphosate. There was a negligible difference between the two CO2 concentrations for the plant dry biomass reduction over the control treatment. CONCLUSIONS: P. hysterophorus growth and reproductive potential (indicated by number of flowers) improved significantly by CO2 enrichment but there was little effect on the overall efficacy of glyphosate applied to control this species.