Effects of CO2 and N on total plant biomass over time

Figure 1: Effects of CO₂ and N on total plant biomass over time. A:Total plant biomass (above-ground plus 0-20 cm below-ground) and carbon at ambient and elevated CO₂ x N levels from 1998 to 2003. Data were pooled across diversity treatments, and each point shows the annual mean (plus standard error) of 74 plots sampled twice per year. There was a significant interaction (Table 1) between CO₂, N and year (P = 0.0013), plus significant main effects (P < 0.05) of year, CO₂ and N. Open circles, ambient CO₂ and ambient N; filled circles, elevated CO₂ and ambient N; open triangles, ambient CO₂ and enriched N; filled triangles, elevated CO₂ and enriched N. B: The effect of CO₂ on total biomass: the CO₂ enhancement (assessed as (value at elevated CO₂) minus (value at ambient CO₂)) at ambient (circles) and enriched (triangles) N supply each year. C: The effect of N availability on the CO₂ biomass effect, defined as the difference between the CO₂ effect at enriched N and that at ambient N, namely (CO₂ effect at enriched N) minus (CO₂ effect at ambient N).