Combined effect of nitrogen fertilization and plant growth-promoting bacteria on growth and nitrogen utilization by lettuce plants.

摘要

The effect of Azospirillum + Pantoea on plant growth and the contribution of biological nitrogen fixation (BNF) by Azospirillum to the plant N budget were studied in lettuce grown at different N levels. Plants (Lactuca sativa L. 'Little Gem Ferro') were grown in a growth chamber (25/15 degrees C for a 16/8 h light/dark cycle and relative humidity of 60/80%) and treated with BiopronReg. (15 g containing 109 CFU.g-1 Azospirillum brasilense and Pantoea dispersa), and then irrigated at four different N levels (0, 1, 3 and 7 mM NO₃-). Bacteria application increased shoot weight, the shoot/root ratio, plant N concentration and N uptake, regardless of N treatment. The effect of bacteria application on root development was dependent on N application. The assimilation of fixed N was estimated, using the 15N natural abundance method, from the difference in delta 15N values between bacteria-treated plants and non-treated plants for each NO₃- level. Significant transfer of nitrogen from BNF to the plant by Azospirillum was observed. The extent of the contribution of BNF to the plant N budget depended on the additional NO₃- supply. The results showed that bacteria have a potential to supply a considerable amount of N to lettuce plants, as well as to stimulate plant growth.