The influence of Rhizobium and arbuscular mycorrhizal fungi on nitrogen and phosphorus accumulation by Vicia faba.
OBJECTIVE
The aim of this study was to investigate the effects of the interactions between the microbial symbionts, Rhizobium and arbuscular mycorrhizal fungi (AMF) on N and P accumulation by broad bean (Vicia faba) and how increased N and P content influence biomass production, leaf area and net photosynthetic rate.


METHODS
A multi-factorial experiment consisting of four different legume-microbial symbiotic associations and two nitrogen treatments was used to investigate the influence of the different microbial symbiotic associations on P accumulation, total N accumulation, biomass, leaf area and net photosynthesis in broad bean grown under low P conditions.


RESULTS
AMF promoted biomass production and photosynthetic rates by increasing the ratio of P to N accumulation. An increase in P was consistently associated with an increase in N accumulation and N productivity, expressed in terms of biomass and leaf area. Photosynthetic N use efficiency, irrespective of the inorganic source of N (e.g. NO3- or N2), was enhanced by increased P supply due to AMF. The presence of Rhizobium resulted in a significant decline in AMF colonization levels irrespective of N supply. Without Rhizobium, AMF colonization levels were higher in low N treatments. Presence or absence of AMF did not have a significant effect on nodule mass but high N with or without AMF led to a significant decline in nodule biomass. Plants with the Rhizobium and AMF symbiotic associations had higher photosynthetic rates per unit leaf area.


CONCLUSIONS
The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.
Jia
Yinsuo
Y
School of Molecular and Cell Biology, University of the Witwatersrand, Private bag 3, Wits 2050, Johannesburg, South Africa.
Gray
Vincent Myles
VM
Straker
Colin John
CJ
D018533:Biomass; D038821:Mycorrhizae / Q000254:growth & development*; D009584:Nitrogen / Q000378:metabolism* / Q000494:pharmacology; D010758:Phosphorus / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D018517:Plant Roots / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D018547:Plant Stems / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D012231:Rhizobium / Q000254:growth & development*; D013559:Symbiosis / Q000187:drug effects; D031307:Vicia faba / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology
D010758:Phosphorus; D009584:Nitrogen