Species-specific reactions to elevated CO₂ and nutrient availability in four grass species

The objective of this study was to determine effects of elevated CO₂ and soil nutrient availability on growth and plant tissue quality in four grass species, Agrostis stolonifera, Anthoxanthum odoratum, Festuca rubra and Poa pratensis, native in Western European calcareous grassland. Plants were grown for 65 days in the greenhouse in pots with untreated soil from calcareous grassland under ambient (350 ppm) and elevated (700 ppm) CO₂ either with or without fertilisation. In general, elevated CO₂ increased plant height, total biomass, starch and sugar concentrations, and decreased water and nitrogen concentrations. However, the response to CO₂-enrichment depended strongly on the grass species investigated. Fertilisation enhanced most effects of elevated CO₂ Biomass production in fertilised plants increased more under elevated CO₂ than in unfertilised plants whereas leaf nitrogen concentration of fertilised plants decreased more at elevated CO₂ than it did in unfertilised plants. Furthermore, a species-specific response to elevated CO₂, depending on soil nutrient availability was detected in starch and sugar concentrations (three-way interaction). The data from this study indicate that grass species vary in their response to elevated CO₂ in biomass production and tissue quality. Furthermore, increasing nutrient availability can substantially alter effects of elevated CO₂. Since the investigated grass species are important larval food-plants of insect herbivores on calcareous grassland, the observed species-specific reactions to CO₂-enrichment and high nutrient availability in tissue quantity and quality are discussed with respect to their effects on insect performance and thus abundance and biodiversity of these insects.