Does elevated CO2 in a changing landscape alter the invasiveness potential of known New England invasives?

Background/Question/Methods: Anthropogenic environmental changes include increased landscape fragmentation in a CO₂-enriched atmosphere that may increase species invasiveness.  Land fragmentation increase light availability by creating open fields and forest edges that provide disturbed habitat for invasive species.  Because the direct effects of elevated CO₂ on plant growth is species specific, and enhanced CO₂ can mitigate other environmental stresses, we wanted to assess the potential response of invasive species in projected future environments to better forecast their future ranges.  Using a multi-factorial design, we compared pairs of invasive and native species from New England that were grown in controlled environment growth chambers at the Duke University Phytotron. Two species of each biennials, vines, and shrubs were used to assess if invasive of various growth forms respond similarly.  After germination, small seedlings were grown at current ambient (380 µmol mol^-1) and elevated CO₂ (580 µmol mol^-1) at three irradiance levels (full sunlight, 1000 µmol PAR m^-2 s^-1; edge, 400 µmol PAR m^-2 s^-1; low, 100 µmol PAR m^-2 s^-1) and two water regimes (field capacity [FC] and 25% FC) for a full growing season.  For the shrubs, growth was measured non-destructively; for the vines and biennials, the plants were also harvested at the end of one growing season.
Results/Conclusions: Preliminary analysis shows that the relative increase in stem length with CO₂ was greater for the native Lindera sp than for invasive Berberis in full sunlight when well-watered.  However elevated CO₂ enhanced Berberis’s length from 100% to 300% in water-stressed conditions and limited light.   Elevated CO₂ did not affect stem length for vines species although stem dry weight was significantly enhanced by elevated CO₂, particulary in edge or low light.  The results show that, an average, the invasive species were more responsive than native species to CO₂ and the enhancement was more pronounced in water-stressed or limited light environments.  These data suggest that the future range and competitiveness of invasive species will be altered by CO₂ interactions.