Effect of CO2enrichment and nitrate application on vegetative growth and dinitrogen fixation of wild and cultivated soybean varieties

Abstract

A wild soybean variety (Glycine soja Sieb. and Zucc. line Nakei-No. 1) and a cultivated soybean variety (Glycine max L. Merr. cv. Tamahomare) were subjected to CO2enrichment and/or NO3-N application (50 and 300 ppm), and the growth and dinitrogen fixation in the vegetative growth stage were examined. 1. The whole plant weight of the cultivated soybean variety was more promoted by CO2enrichment than by NO3-N application, while that of the wild one was enhanced by NO3-N application compared with CO2enrichment. 2. The dinitrogen-fixing activity which was lower in wild soybean variety than in the cultivated one increased by CO2enrichment in both soybean varieties, when nitrate was not applied to the plants. The increase by CO2enrichment was remarkable in the cultivated soybean variety and was negligible in the wild one. In both soybean varieties, the dinitrogen-fixing activity decreased by the application of 50 ppm NO3-N and recovered approximately to the same level as that in the plants which did not receive NO3-N as a result of CO2enrichment. 3. The increment of whole plant N in the cultivated soybean variety was markedly enhanced by either CO2enrichment or NO3-N application, while that in the wild soybean variety was slightly enhanced by NO3-N application and did not change by CO2enrichment. However, the simultaneous supply of CO2and NO3-N enhanced remarkably the increment of whole plant N in both soybean varieties. These results indicate that the CO2enrichment increased the dry matter production in the cultivated soybean variety along with the increase of dinitrogen-fixing activity, while in the wild one dry matter production increased slightly. On the other hand, the increase of dry matter production by NO3-N application was less appreciable in the cultivated soybean variety but larger in the wild one compared with the increase by CO2enrichment, respectively. The simultaneous supply of CO2and NO3-N increased remarkably the dry matter production in both soybean varieties. Therefore, it is assumed that the vegetative growth of the cultivated soybean variety is predominantly limited by the insufficient supply of photosynthates, whereas that of the wild one is mainly limited by the insufficient supply of N due to lower dinitrogen fixation by nodules. © Taylor & Francis Group, LLC.