Arbuscular mycorrhizas in phosphate-polluted soil: interrelations between root colonization and nitrogen

To investigate whether arbuscular mycorrhizal fungi (AMF) - abundant in a phosphate-polluted but nitrogen-poor field site - improve plant N nutrition, we carried out a two-factorial experiment, including N fertilization and fungicide treatment. Percentage of root length colonized (% RLC) by AMF and tissue element concentrations were determined for four resident plant species. Furthermore, soil nutrient levels and N effects on aboveground biomass of individual species were measured. Nitrogen fertilization lowered % RLC by AMF of Artemisia vulgaris L., Picris hieracioides L. and Poa compressa L., but not of Bromus japonicus Thunb. This - together with positive N addition effects on N status, N:P-ratio and aboveground biomass of most species - suggested that plants are mycorrhizal because of N deficiency. Fungicide treatment, which reduced % RLC in all species, resulted in lower N concentrations in A. vulgaris and P. hieracioides, a higher N concentration in P. compressa, and did not consistently affect N status of B. japonicus. Evidently, AMF had an influence on the N nutrition of plants in this P-rich soil; however - potentially due to differences in their mycorrhizal responsiveness - not all species seemed to benefit from a mycorrhiza-mediated N uptake and accordingly, N distribution.