CLONAL GROWTH TRAITS OF 2 PRUNELLA SPECIES ARE DETERMINED BY COOCCURRING ARBUSCULAR MYCORRHIZAL FUNGI FROM A CALCAREOUS GRASSLAND

1 The effects of three different isolates of co-occurring arbuscular m ycorrhizal fungi (AMF) from the same calcareous grassland on clonal gr owth traits of Prunella vulgaris and P. grandiflora were investigated. 2 P. vulgaris and P. grandiflora were found to be highly dependent on AMF for growth in soil from the same calcareous grassland. The additi on of phosphorus did not significantly increase the growth of either n onmycorrhizal or mycorrhizal P. vulgaris. 3 The three AMF isolates dif fered significantly in their effects on size of the two plant species. The AMF isolates also differed in their effects on stolen branching a nd stolen length and here the effects were not the same in the two pla nt species, The differential effects of AMF isolates on clonal growth traits were consistently independent of the level of AMF colonization throughout the experiment, indicating that the effects were not due to different rates of colonization. Some of the AMF isolate effects on s tolen branching in P. vulgaris is were also independent of the effects of AMF isolates on plant size. These results suggest that different A MF in a natural community have the potential to influence the growth, number of ramets and distribution of ramets in Prunella populations. 4 The strong differential effects of AMF isolates on clonal growth trai ts of P. vulgaris occurred in a homogeneous environment. Plasticity in such traits has previously been considered important for efficient re source foraging in a heterogeneous environment. Our results, however, indicate that different AMF in a community could strongly influence re source foraging strategies in clonal plants irrespective of environmen tal heterogeneity. The results also suggest that increasing the availa bility of phosphorus would be unlikely to alter these effects. 5 Our r esults point strongly to the potential importance of AMF diversity as a determinant of plant population structure in ecosystems.