Nitrogen uptake and growth of white clover inoculated with indigenous and exotic Rhizobium strains

Abstract

Little information is available on investigating the effectiveness of indigenous and exotic rhizobia in enhancing nitrogen uptake and growth of white clover. This study aimed to evaluate the nitrogen fixation effectiveness of native rhizobia isolated from white clover grown in Taiwan as compared to an exotic strain, Rhizobium leguminosarum bv. trifolii BCRC 14266. Indigenous rhizobia were isolated from nodules in roots of white clover, and 16S rRNA gene sequences were used to identify their taxonomy. To compare the symbiotic effectiveness of indigenous and exotic rhizobia, white clover plants were inoculated respectively with two indigenous isolates (CHB 1120 and CHB 1121), BCRC 14266, and a non-inoculated control. Based on 16S rRNA gene sequences, CHB 1120 and CHB 1121 could be identified as Rhizobium species. Compared with the non-inoculated control and BCRC 14266, CHB 1120 and CHB 1121 significantly increased the dry weight of shoots and roots at 75 days after planting (DAP). Additionally, CHB 1120 and CHB 1121 significantly enhanced the amount of chlorophyll present in leaves estimated by SPAD readings, increasing nitrogen contents in shoots by 38.1 and 49.2%, respectively. In comparison with BCRC 14266, CHB 1120 and CHB 1121 significantly increased the nodule number and nitrogenase activity at both 45 and 75 DAP. In conclusion, the two indigenous strains significantly outperform the exotic strain and non-inoculated control in promoting nitrogen uptake and growth of white clover.