What was done
After five-years of exposure to atmospheric CO2 concentrations of 350 and 650 ppm in a FACE experiment, plant material consisting of leguminous and non-leguminous species common to calcareous grasslands of Switzerland were harvested and fed to terrestrial slugs to determine if they preferred eating plants grown in one of the two CO2 treatments more than the other.  In addition, the authors wanted to learn if slugs needed to consume greater amounts of CO2-enriched plant material as opposed to ambiently-grown vegetation, which has been reported in the literature for some herbivores.

What was learned
Elevated CO2 had little effect on the feeding habits of slugs.  Total plant consumption, for example, was similar for slugs feeding upon CO2-enriched and ambiently-grown vegetation.  When fed a mixture of legumes, slugs exhibited no preferences between available plant species.  Similarly, when fed a mixture of non-legume species, slugs also showed no selective feeding preferences.  However, when fed a combination of both leguminous and non-leguminous species, slugs displayed a marginally significant preference for legumes.

What it means
As the atmospheric CO2 concentration continues to increase, it is likely that slugs residing in calcareous grasslands of Switzerland will continue to exist in such ecosystems without altering their total consumption of plant material.  Thus, this herbivore will likely not exhibit any compensatory feeding response to atmospheric CO2 enrichment - in a possible attempt to increase its nitrogen uptake - but may exhibit a slight shift in its feeding preference to leguminous species to possibly offset any CO2-induced reductions that might occur in foliar nitrogen concentration.