Can Gas-Exchange Characteristics help Explain the Invasive Success of Lythrum salicaria?

Abstract

Since its introduction to North America, Lythrum salicaria (L.) (purple loosestrife) has become invasive in marshy and riparian habitats. We compared gas-exchange responses to external CO2 partial pressure and light, as well as related leaf structural and biochemical characteristics, of L. salicaria with those of co-occurring native Asclepias syriaca (common milkweed) and Solidago graminifolia (lance-leaved goldenrod) along a pond bank in the Black Rock Forest, Cornwall, New York, USA to examine if the invasive success of L. salicaria may be influenced by robust leaf gas-exchange characteristics, including relatively high rates of photosynthesis and low rates of respiration, compared with those of less successful co-occurring native plant species. Neither the mean rate of net photosynthesis measured at ambient CO2 and saturating photon flux density (A) nor the mean dark respiration rate (RD) differed significantly between L. salicaria and either of the native species, while both the mean maximum rate of photosynthesis at saturating CO2 concentration and photon flux density (Amax) and the mean rate of respiration measured in light (RL) were significantly higher inL. salicaria thanA. syriaca, but no different betweenL. salicaria and S. graminifolia. Likewise, photosynthetic nitrogen-use efficiency was greater in L. salicaria than A. syriaca only, while photosynthetic water-use efficiency was significantly less in bothL. salicaria andS. graminifolia than in A. syriaca. Despite limited interspecific differences in leaf photosynthesis, respiration, and resource-use efficiency, particularly between L. salicaria and S. graminifolia, we found that L. salicaria assimilated 208% more carbon per unit of energy invested in leaf biomass than either of the co-occurring native species, suggesting that increased photosynthetic energy-use efficiency may influence its observed invasive success.