Elevated CO2 increases energy-use efficiency of invasive Wedelia trilobata over its indigenous congener

Increasing atmospheric CO₂ concentration is regarded as an important factor facilitating plants invasions by stimulating invasive species growth. However, the physiological mechanisms by which invasive plants increase at the expense of existing native plants are poorly understood. Plant growth is always related to energy-use process including energy assimilation and expenditure, and thus examination of energetic properties could provide mechanistic insight into growth responses to increased CO₂. The aims of this study were to examine the effect of rising CO₂ on the growth and energetic properties of alien invasive species (Wedelia trilobata (L.) Hitchc.) and its native congener (Wedelia chinensis (Osbeck.) Merr.) in South China, and to determine if the specific energetic properties of invasive species at elevated CO₂ favoring its growth. Elevated CO₂ stimulated a greater increase in biomass production for invasive W. trilobata (58.9%) than for its indigenous congener (48.1%). Meanwhile, elevated CO₂ altered the energetic properties differently upon species. For invasive W. trilobata, elevated CO₂ significantly increased total energetic gain via photosynthetic activity (A _total), but decreased energetic cost of biomass construction (CC), and thus enhanced photosynthetic energy-use efficiency (PEUE) by 85.3%. In contrast, the indigenous W. chinensis showed a slight increase in PEUE by 43.8%. Additionally, W. trilobata individuals grown in elevated CO₂ increased energy allocation towards stems. Statistic analysis revealed significant associations between growth characteristics (relative growth rate and biomass) and energetic properties (CC and PEUE), suggesting the greater growth stimulation in invasive species could be partly explained by its specific energetic properties in elevated CO₂ concentration. The invasive species showed a greater increase in energy-use efficiency under elevated CO₂, which consequently facilitated its growth. It might be a physiological mechanism promoting success of invasion with ongoing increase in atmospheric CO₂ concentration.