The role of phosphorus deficiency in nodule microbial composition, and carbon and nitrogen nutrition of a native legume tree in the Cape fynbos ecosystem

摘要

In phosphorus (P)-poor ecosystems, microbial communities can play a major role in the nitrogen (N) mineral nutrition during N-2 fixation in legumes. This study investigated the role of P nutrition on the composition of N-2-fixing bacterial community in Virgilia divaricata root nodules, grown under glasshouse conditions. V. divaricata seeds were germinated in Fynbos soil as a natural inoculum, and, thereafter, transferred into sterile quartz-sand cultures and supplied with 500 mu M P and 5 mu M P, respectively. The N-2-fixing bacterial communities in the rhizosphere and root nodules were examined on the basis of the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) banding patterns of 16S rDNA and sequencing methods. The GenBank blast results showed that V. divaricata was nodulated by a wide range of root-nodule bacterial strains also found in the rhizosphere. These included Burkholderia phytofirmans, Burkholderia sp. and Bradyrhizobium sp., during both high and low P supply. The N-15 natural-abundance data also confirmed that 40-50% of the N nutrition was from symbiotic N-2 fixation. This is not only evidence of nodulation, but an indication of the adaptation of a range of N-2-fixing bacterial strain species to the nutrient-poor, sandy, acidic soil of the Mediterranean-type ecosystems of the fynbos vegetation in the Cape Floristic Region (CFR). Legume species V. divaricata is highly adapted to the low-nutrient soils of its native range by its association with the symbiotic N-2-fixing bacteria.