Difference in isotope exchange between microcosm sides, in dependence of relative AMF qualities.

Relative AMF quality is either quantified as the GCA difference for shoot *P or total shoot P (see Methods for details). Relative ¹⁴C transfer is quantified as the difference in ¹⁴C allocation between microcosm sides with different AMF species. A positive slope indicates that C allocation is biased towards the side with the higher-quality AMF. ¹⁴C:*P quantifies the P costs in units of C. A negative slope indicates that these are lower on the side with the higher-quality AMF. Solid lines and gray areas indicate linear regression lines and standard errors. Open symbols indicate compositions containing the AMF Claroideoglomus claroideum for which short-term and long-term quality (assessed as *P transfer to shoots and total shoot P accumulation, respectively) differed substantially (see Methods for details).