Biological Response of Invasive Parthenium Weed to Elevated Concentration of Atmospheric Carbon Dioxide and Soil Salinity

Climate change elements including elevated atmospheric carbon dioxide (CO 2 ) concentration and soil salinity significantly impact weed biology and management. In this study, we evaluated the performance of a highly invasive plant species, parthenium weed ( Parthenium hysterophorus L.) grown at various soil salinity levels (ranging from 0 to 16 dS m −1 ) at two CO 2 concentrations (ambient: 400 ppm and elevated: 700 ppm). The CO 2 concentration and soil salinity individually affected various early growth attributes of parthenium weed. The interaction between CO 2 and salinity was significant for chlorophyll index, stem dry weight and phenolics content. Parthenium weed plants grew taller (13%), achieved greater leaf area (28%) and produced more dry weight (24%) when raised under elevated as compared with the ambient CO 2 . Soil salinity had a dose-dependent, negative effect on various growth attributes, chlorophyll index, relative water content and phenolics content. Even the modest levels of salinity (4.2 to 4.6 dS m −1 ) caused 50% reduction in dry weights of leaves, roots and whole plants. Sodium ion (Na + ) concentration peaked at the highest salinity level (16 dS m −1 ) as compared with the lower salinity levels (0 to 12 dS m −1 ). Overall, salinity had a negative effect on different growth variables but elevated CO 2 improved growth and phenolics content regardless of the salt stress regime. Hence, parthenium weed could benefit from future atmospheric CO 2 concentration and may invade some salt-affected areas.