Global environmental changes such as increasing atmospheric CO₂ and temperature may influence invasion dynamics in complex ways.  Garlic mustard (Alliaria petiolata) is a widespread, invasive biennial whose responses to future climate scenarios are not well understood.  In a growth chamber study, A. petiolata and the co-occurring native Geum vernum were grown separately from seed in a factorial design under ambient and elevated (+ 3 ^oC) spring temperatures, and ambient and elevated atmospheric CO₂ conditions (380 vs. 550 ppm).  Measurements included total biomass, leaf expansion rates, gas exchange, and leaf concentrations of allelopathic compounds for A. petiolata. 

Results/Conclusions

Both species grew significantly faster at high temperatures than at ambient temperatures as measured by leaf expansion, but the total biomass of A. petiolata was reduced in the high temperature treatments, possibly due to increased root respiration.  The elevated CO₂ treatment had only slight effects on growth, but increased leaf thickness significantly in both species, and A. petiolata showed photosynthetic down-regulation at high CO₂.  Concentrations of flavonoids and cyanide decreased significantly in A. petiolata leaves at elevated CO₂, possibly due to dilution by starch accumulation or resource limitation.  Glucosinolate concentrations did not differ significantly among treatments.  These data suggest that warm temperatures will be more important stimulants of early spring growth for A. petiolata and G. vernum than elevated CO₂ and that there may be reduced allelopathy in A. petiolata in future climate scenarios.