EFFECTS OF DOUBLED CO2 ON SOYBEAN(BRAGG) NODULATING MUTANTS CULTIVATED IN NITROGEN-FREE MEDIUM

Effects of doubled CO2 on soybean(Bragg) nodulating mutants grown in nitrogen-free medium were studied in the open-top chambers. The main results were described as follows: Under no-nitrogen condition, doubled CO2 remarkably raised soybean biomass,and increased the number and weight of nodules per plant, but the effects on nitrogenase activities were different as the seedlings growing up. The results of sample 25 days seedling showed that doubled CO2 sharply stimulated specific nitrogen-fixing activity(SNA) and total nitrogen-fixing activity(TNA). In the following 3 days, such phenomena wasn't found, on the contrary SNA was decreased. In two CO2 levels. TNA was higher in nts382 than in Bragg, but SNA was lower slightly in the fomer than in the latter. The difference between two samplings indicated that the response of plant to doubled CO2 were influenced by sampling time and plant growth stages. and showed that this Stimulation couldn't maintain permanently in the mutant.It was suggested that in the CO2 doubled environment. symbiotic nitrogrn-fixing plants could play a more important role in nitrogen balance in one ecosystem. on the other hand, legume crops could be improved through breedings in the future.