Different responses of Molinia caerulea plants from three origins to CO2 enrichment and nutrient supply

The global environmental change factors eutrophication and CO2 enrichment will affect carbon and nutrient cycling in plants and ecosystems. In order to study their interactions on plant performance, growth chamber experiments were performed with plants from three origins of the common but ecologically variable Purple Moor Grass (Molinia caerulea (L.) Moench) grown in a bi-factorial combination of two levels of nutrients (for N: 31 or 62 kg ha−1 year−1) and CO2 (400 or 600 μmol mol−1 CO2). Plants were established from ramets with known start weights so that total biomass accumulation of each plant over time could be analysed. Plant phenology, leaf properties and the biomass of different fractions (inflorescences, leaves, stems and rootstocks) were investigated to identify treatment effects on plant development and allocation patterns. The few consistent responses identified in the plants were a significant increase in leaf biomass by doubling the nutrient supply and plants exposed to elevated CO2 showing a reduced specific leaf area (SLA), an increased number of senescent leaves and increased rootstock growth. Increasing the nutrient supply had greater effects on aboveground biomass than raising the CO2 concentrations but significant interactions between the two plant fertilisers were absent. The variable responses of the ramets to the addition of resources were largely modified by their phenology and their readiness to switch from vegetative to reproductive growth. We conclude that differences in phenology and ecological behaviour of ecotypes of the same plant species will largely affect their response to environmental change.