Rhizobia in tropical legumes—XIV. Ion uptake differences between fast- and slow-growing strains

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We compared the uptake of nitrogen, potassium and phosphorus (as well as 14C-labelled mannitol, 3H-labelled glutamate, and 32P-labelled phosphate) in three fast- and three slow-growing rhizobia. The fast-growing strains used were Rhizobium meliloti (isolated from Medicago sativa), R. trifolii (from Trifolium subterraneum), and Rhizobium spp from Leucaena leucocephala, while the slow-growing strains were R. japonicum (Glycine max), and two Rhizobium spp (from Centrosema pubescens and Crotolaria anagyroides). Slow-growing organisms preferentially utilized glutamate in the medium. Both fast- and slow-growing strains took up more NH + 4-N than NO − 3-N on a per cell basis. In the presence of mannitol, fast-growing strains can cause either acid or alkaline reactions, an effect that is dependent only on the N-source (NH + 4 or NO − 3). Uptake preferences of the fast-growing Leucaena isolate (UMKL 19) resembled those of the slow-growing rhizobia, further strengthening the argument that this organism (and others like it) may be intermediate between the normal fast- and slow-growing groups. Generally, the efficiency of uptake of N (either as NH + 4 or NO − 3), P, and therefore K, was greater in the fast-growing organisms.