Responses of invasive and native plant species to drought stress and elevated CO2 concentrations: a meta-analysis

Superior trait responses of invasive plant species to their native counterparts determine invasion success under various environmental conditions. To date, numerous experimental studies have compared the physiological and growth trait responses of invasive plant species to native ones in simulated drought or CO2 enrichment conditions; however, these studies have not recently been summarised. Here, we conducted a global meta-analysis using 48 experimental studies to determine whether there are generalisable differences between invasive and native plant species in terms of their physiological and growth trait responses to drought and elevated CO2 and which traits potentially facilitate plant invasion in these conditions. The results indicate that the magnitude of responses do not differ substantially between invasives and natives for most traits under drought or elevated CO2. Under drought stress, the photosynthetic rate, stomatal conductance, shoot biomass and total biomass decreased in both plant groups, supporting the contention that plants, irrespective of their origin, are negatively affected in water-limited environments. By contrast, we found that elevated CO2 increased water-use efficiency, shoot biomass and total biomass and decreased stomatal conductance in both invasives and natives, indicating that both plant groups grow vigorously in such conditions. Compared with estimates for natives, invasives were taller and invested more biomass to roots under drought and showed greater allocation to shoot biomass under elevated CO2. Although there were no substantial differences in the magnitude of responses in most studied traits, the differential growth responses in invasives may confer an advantage over natives under decreased water availability and high CO2 concentrations.