Performance and allocation patterns of the perennial herb, Plantago lanceolata, in response to simulated herbivory and elevated CO₂ environments

Summary

We tested the prediction that plants grown in elevated CO₂ environments are better able to compensate for biomass lost to herbivory than plants grown in ambient CO₂ environments. The herbaceous perennial Plantago lanceolata (Plantaginaceae) was grown in either near ambient (380 ppm) or enriched (700 ppm) CO₂ atmospheres, and then after 4 weeks, plants experienced either 1) no defoliation; 2) every fourth leaf removed by cutting; or 3) every other leaf removed by cutting. Plants were harvested at week 13 (9 weeks after simulated herbivory treatments). Vegetative and reproductive weights were compared, and seeds were counted, weighed, and germinated to assess viability.

Plants grown in enriched CO₂ environments had significantly greater shoot weights, leaf areas, and root weights, yet had significantly lower reproductive weights (i.e. stalks + spikes + seeds) and produced fewer seeds, than plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plants grown in ambient CO₂ environments. Relative biomass allocation patterns further illustrated differences in plant responses to enriched CO₂ atmospheres: enriched CO₂-grown plants only allocated 10% of their carbon resources to reproduction whereas ambient CO₂-grown plants allocated over 20%. Effects of simulated herbivory on plant performance were much less dramatic than those induced by enriched CO₂ atmospheres. Leaf area removal did not reduce shoot weights or reproductive weights of plants in either CO₂ treatment relative to control plants. However, plants from both CO₂ treatments experienced reductions in root weights with leaf area removal, indicating that plants compensated for lost above-ground tissues, and maintained comparable levels of reproductive output and seed viability, at the expense of root growth.