Abstract
INTRODUCTION: Soil phosphorus (P) deficiency limits plant growth and productivity in grassland ecosystems and may moderate the growth-promoting effects of "carbon dioxide (CO(2)) fertilization effect". METHODS: To evaluate the interactive effects of these two factors on the growth and physiology for annual ryegrass (Lolium multiflorum 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(2) (400 and 800 μmol mol(-1), respectively). RESULTS: Elevated [CO(2)] 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(0.004), P(0.02), and P(0.06). Two-way ANOVA results showed that CO(2) × P (p < 0.001) significantly affected stomatal traits, leaf photosynthesis and biomass. The stimulation of growth and photosynthesis by elevated CO(2) concentration (e[CO(2)]) was reduced or highly suppressed, indicating that the sensitivity of annual ryegrass to P deficiency was enhanced under e[CO(2)]. DISCUSSION: These results indicated that P limitation may offset the positive effects of e[CO(2)] on plant growth by altering stomatal traits, leaf photochemical processes and biochemical composition in annual ryegrass.