To better understand the ecology of arbuscular mycorrhizal (AM) symbiosis, we need
to measure functional traits of individual fungal virtual taxa under field conditions.
The efficiency of AM fungi in locating nutrient-rich patches in soil space is one of
their central traits in this symbiotic relationship. We used plots of a long-term field
experiment in grassland with manipulated functional group composition of host plant
community to establish ingrowth patches with substrate free of roots and fungi and
with varying nutrient availability. Comparison of the original AM fungal community
before patch creation with that present 9 weeks after patch establishment enabled
us to estimate relative hyphal foraging speed for 41 fungal taxa, and a comparison of
the fungal community in neighbouring patches differing in nutrient availability provided
estimates of hyphal foraging precision for 22 taxa. Members of two dominant
fungal families, Glomeraceae and Claroideoglomeraceae, differed in their foraging
speed and precision. Glomeraceae taxa responded more slowly, but with a higher
focus on enriched patches. We further demonstrated the usefulness of the obtained
fungal functional traits by testing the differences between grass and dicotyledonous
plant hosts using a data set obtained in another experiment at the same plots. Grass
species hosted AM fungal communities with higher foraging speed, but lower foraging
precision than the dicotyledonous species. Our study results support the use of
field experiments for measuring comparative characteristics of AM fungi, which are
highly elusive (or misrepresented) under controlled conditions.