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Figure 4.39 Benefit of nitrogen fixation in legumes depending on N fertilisation. Total nitrogen content (A) and plant biomass (B) of subclover (Trifolium subterraneum) plants grown in a glasshouse for four weeks in the presence and absence of nitrogen fertiliser (10 mM potassium nitrate, ‘N’) and/or the rhizobium symbiont (Rhizobium leguminosarum bv. trifolii, ‘R’). Plants benefit from rhizobial inoculation only in the absence of N fertilizer, as shown by the increases in N content and biomass. Rhizobia confer a similar benefit to the unfertilised subclover plants as a 10 mM nitrate addition does, although this varies with different rhizobial strains and with legume species. (Data modified from C.-H. Goh et al., Plant Cell Environ, 2015)