[Responses of Onobrychis viciaefolia Scop and soil nitrogen contents to elevated atmospheric CO2 concentration]

The effects of elevated CO2 on terrestrial ecosystem processes are highly related to the N cycling in the ecosystem. In two closed chambers with different CO2 concentration (ambient CO2 355 - 370 micromol x mol(-1), and elevated CO2 700 micromol x mol(-1)), pot experiments were conducted to study the responses of Onobrychis viciaefolia Scop and soil nitrogen contents to elevated CO2. The results showed that compared with ambient CO2, elevated CO2 increased the plant dry biomass by 25.1% (P < 0.01), but decreased the plant N concentration by 25.3% (P < 0.001), resulting in little change of total plant N. After three months experiment, soil total N, NO3 (-) -N and NH4 (+) -N under both ambient and elevated CO2 conditions decreased, while soil microbial biomass N increased significantly. Soil NH4 (+) -N concentration had little difference under ambient and elevated CO2 conditions, but under elevated CO2 condition, soil NO3 (-) -N concentration decreased significantly, while microbial biomass N increased significantly. By the end of the experiment, the total N content of whole soil-plant ecosystem had a slight increase, especially under elevated CO2 condition, which was probably due to the higher N-fixation capability of O. viciaefolia Scop under CO2 enrichment.