Non-native species have advantageous traits even in low CO2 levels

Background/Question/Methods

CO2 is a critical component in plant growth; rapid increases in global CO2 levels have motivated numerous studies on the effects of plant responses at high CO2 levels. However, fewer studies have been conducted on the effects of low CO2 to study plant responses prior to the industrial revolution. Studying plant responses to low CO2 could be instrumental in understanding future plant responses to rising CO2 levels and what traits or strategies underlie these responses. Here, we investigated the effects of pre- and post-industrial CO2 levels on nine common herbaceous plants (three native, six non-native). Nutrients have been shown to constrain plant response to CO2, so we also compared the effects of high nutrients and no nutrients under each CO2 treatment. Plant physiological traits (eg. leaf physiology, total biomass, and root/shoot biomass allocation) were measured as indicators of plant response to changing resource availability. We tested the following hypotheses: (1) non-native species respond more strongly to increasing resource availability, (2) variation in leaf traits, such as photosynthetic rate and stomatal conductance, is connected to growth differences, and (3) low nutrients constrain plant responses to CO2 regardless of native/non-native status.

Results/Conclusions

As expected, the 200 ppm treatment reduced growth to varying degrees across all species. Non-native species responded the strongest to increasing resource availability with higher relative growth rates compared to native species. Non-native species had higher stomatal conductance rates and similar photosynthetic rates when compared to native species in the low CO2 treatment. Non-native species and those that had higher stomatal conductance in the 200 ppm treatment had higher relative growth rates. While CO2 was shown to be an important variable, this effect interacted strongly with nutrient availability. These results indicate that non-native plants have advantageous traits that contribute to maintaining high growth rates at low CO2 and will also most likely help them as CO2 levels continue to increase; however, nutrient availability will likely be even more important in a high CO2 world.