We controlled arbuscular mycorrhizal (AM) fungi in the routs of bluebell (Hyacinthoides non-scripta L. Chouard ex Rothm.) in the field by immersina otherwise undisturbed colonies in a fungicide suspension. Monthly application of benomyl successfully reduced root colonization by AM fungi throughout a 2 yr experimental period. Benonlyl had lit) effect on the availability of soil phosphorus (P), but reduced the P concentration of all parts of the plant (bulb, roots, leaves and inflorescences). Unlike the vegetative parts, flowers and seed of benomyl-treated plants had the same P concentration as untreated plants at the end of the first season. However, at the final harvest after two growing seasons flower P concentration had been reduced by treatment. H. non-scripta appears to protect reproductive structures from P deficiency when the plant is deprived of P, suggesting that A.M plays an important role in fitness determination. This is the first demonstration that depriving a plant growing in its natural environment of mycorrhiza on a long-term basis can reduce P acquisition. Taken with data from experiments in controlled conditions, it confirms that H. non-scripta is an obligately mycorrhizal species.