Growth yield of Vicia faba L in response to microbial symbiotic associations

A multifactor experiment was undertaken to investigate the influence of Rhizobium and arbuscular mycorrhizal fungi (AMF) on biomass production, leaf area generation, whole plant photosynthetic and respiration rates, growth yield and maintenance respiration in Vicia faba L under low phosphorus (P) supply. Treatments consisted of low (LN) or high nitrogen (HN) supply with or without microbial symbiont(s). Plants were harvested at 54 (T1) and 63 (T2) days after planting. In all instances, plants colonized with both microbial symbionts had significantly higher total biomasses, leaf areas, whole plant photosynthesis and respiration rates than plants with only one or no microbial symbionts. Similarly, plants with both microbial symbionts also had significantly higher (≥ 0.7) growth yield (Yg) values than all the other treatments. There were no significant differences in Yg values between harvest intervals within individual treatments. Maintenance respiration rates were also highest in plants with two microbial symbionts (> 30 CO2 (g DM)− 1 d− 1). In LN plants colonized by both microbial symbionts there was evidence of compensatory increases in the photosynthetic rates in response to the carbon sink demands of the microbial symbionts. Finally, the results of this investigation are consistent with the hypothesis that the plant potential photosynthetic capacity exceeds the carbon demand of the Rhizobium–AMF symbiotic complex.