Innate and evolutionarily increased advantages of invasive Eupatorium adenophorum over native E. japonicum under ambient and doubled atmospheric CO2 concentrations

Both innate and evolutionarily increased ecophysiological advantages can contribute to vigorous growth, and eventually to invasiveness of alien plants. Little effort has been made to explore the roles of innate factors of alien plants in invasiveness and the effects of CO2 enrichment on alien plant invasions. To address these problems, we compared invasive Eupatorium adenophorum, its native conspecific, and a native congener (E. japonicum) under ambient and doubled atmospheric CO2 concentrations. Native E. adenophorum from Mexico grew slower than invasive E. adenophorum but faster than native E. japonicum under both CO2 concentrations. The faster growth rate of invasive E. adenophorum was associated with higher photosynthetic capacity and leaf area ratio. For invasive E. adenophorum, the higher photosynthetic capacity was associated with higher nitrogen (N) allocation to photosynthesis, which was related to lower leaf mass per area; the higher leaf area ratio was due to lower leaf mass per area and higher leaf mass fraction. Tradeoff between N allocations to photosynthesis versus defenses was found. CO2 enrichment significantly increased relative growth rate and biomass accumulation by increasing actual photosynthetic rate for all studied materials. However, the relative increase in growth was not significantly different among them. CO2 enrichment did not influence N allocation to photosynthesis, but increased N allocation to cell walls. The reduced leaf N content decreased N content in photosynthesis, explaining the down-regulation of photosynthetic capacity under prolonged elevated CO2 concentration. Our results indicate that both innate and evolutionary advantages in growth and related ecophysiological traits contribute to invasiveness of invasive E. adenophorum, and CO2 enrichment may not aggravate E. adenophroum's invasion in the future.