Arbuscular mycorrhizal fungi reduce effects of physiological integration in Trifolium repens

BACKGROUND AND AIMS: One of the special properties of clonal plants is the capacity for physiological integration, which can increase plant performance through mechanisms such as resource sharing and co-ordinated phenotypic plasticity when plants grow in microsites with contrasting resource availabilities. However, many clonal plants are colonized by arbuscular mycorrhizal fungi (AMF). Since AMF are likely to reduce contrasts in effective resource levels, they could also reduce these effects of clonal integration on plasticity and performance in heterogeneous environments. METHODS: To test this hypothesis, pairs of connected and disconnected ramets of the stoloniferous herb Trifolium repens were grown. One ramet in a pair was given high light and low nutrients while the other ramet was given high nutrients and low light. The pairs were inoculated with zero, one or five species of AMF. KEY RESULTS: Pairs of ramets grown without AMF developed division of labour and benefited from resource sharing, as indicated by effects of connection on allocation to roots, accumulation of mass, and ramet production. Inoculation with five species of AMF significantly reduced these effects of connection, both by inhibiting them in ramets given high nutrients and inducing them in ramets given high light. Inoculation with one species of AMF also reduced some effects of connection, but generally to a lesser degree. CONCLUSIONS: The results show that AMF can significantly modify the effects of clonal integration on the plasticity and performance of clonal plants in heterogeneous environments. In particular, AMF may partly replace the effects and benefits of clonal integration in low-nutrient habitats, possibly more so where species richness of AMF is high. This provides the first test of interaction between colonization by AMF and physiological integration in a clonal plant, and a new example of how biotic and abiotic factors could interact to determine the ecological importance of clonal growth.