Relative effectiveness of indigenous populations of vesicular-arbuscular mycorrhizal fungi from four sites in the Negev

ABSTRACT Vesicular-arbuscular mycorrhizal (VAM) fungi indigenous in the soil of the semi arid northern Negev of Israel greatly enhanced phosphorus (P) uptake of mycorrhizal pepper plants in three out of four soils tested and at four P levels. In a calcareous loess soil, additions of superphosphate equivalent to 3,000 kg ha−1 could not alleviate the absence of the VAM association. Increasing internal leaf P levels were correlated closely with a stimulation of flower bud production in pepper. Subsequent planting of onion in the same soils with no further P addition revealed the total dependency of this species on the VAM symbiosis. Mycorrhizal infection reduced by half the R/S ratios of onion plants, mainly by the enhancement of shoot growth. Results indicate the presence of a highly efficient VAM population in the loess soil. These findings are considered with regard to the evolution of the mycorrhizal association and its effect on plant morphology and physiological processes.