Effects of elevated carbon dioxide on plant growth and leaf photosynthesis of annual ryegrass along a phosphorus deficiency gradient

Soil phosphorus (P) deficiency limits plant growth and productivity in grassland ecosystems and may moderate the growth-promoting effects of "carbon dioxide (CO ) fertilization effect". To evaluate the interactive effects of these two factors on the growth and physiology for annual ryegrass ( Lam.), plants were grown in controlled growth chambers with a range of P supply (0.004, 0.012, 0.02, 0.06, 0.1 and 0.5 mM) under two levels of CO (400 and 800 μmol mol , respectively). Elevated [CO ] dramatically increased the aboveground biomass and net photosynthetic rates of annual ryegrass by 14.5% and 25.3% under sufficient P supply (0.5 mM), respectively, whereas decreased the belowground biomass and net photosynthetic rates under lower P supply of P , P , and P . Two-way ANOVA results showed that CO × P ( < 0.001) significantly affected stomatal traits, leaf photosynthesis and biomass. The stimulation of growth and photosynthesis by elevated CO concentration ( [CO ]) was reduced or highly suppressed, indicating that the sensitivity of annual ryegrass to P deficiency was enhanced under [CO ]. These results indicated that P limitation may offset the positive effects of [CO ] on plant growth by altering stomatal traits, leaf photochemical processes and biochemical composition in annual ryegrass.