Fig 1.
Plants and AMF were grown in microcosms with plant roots divided between two sides with a central plastic barrier. Mesh membranes (21μm pores) allowed AMF growth throughout each side of the microcosm. Plant roots were restricted to the innermost of the three compartments per side. The plant carbon (C) pool was labeled with 14C, and soil phosphorus (P) pools in the outermost compartments were labeled with either 32P or 33P. 14C transferred from plants to AMF was measured in the outer compartments of the microcosm. Radioactive P (*P) taken up by AMF from outer compartments and transferred to plants was measured in plant shoots. The space between inner and exterior compartments served as a buffer and prevented direct root uptake of applied *P from these outer compartments and direct root exudation of 14C into these outer compartments. Each plant species interacted with a pool of 3 AMF species: there were three choice microcosms with two AMF species and three no-choice microcosms with a single AMF species. Microcosms with 2 AMF species were replicated twice (with reciprocal 32P/33P labeling), resulting in 9 microcosms per host plant species.
Table 1.
Plant and AMF species combinations used in this experiment with their respective taxonomic families.
Fig 2.
We used general combining abilities (GCAs) for (A) shoot radioactive P (*P), and (B) shoot P as indicators of AMF quality (GCAs were estimated using mechanical diallel analyses; S1 Appendix and Methods). Error bars are ± 1 s.e. of the mean. AMF species are indicated by their genus; see Table 1 for full names.
Fig 3.
Dependence of radioisotope data on the relative quality of AMF.
AMF quality was determined as general combining ability (GCA) using diallel analysis, for shoot radio-P (*P) and total shoot P (P). Radioisotope data refer to microcosm halves, i.e. they characterize the C and P exchange that occurs with each AMF species in each plant × AMF species composition. Solid regression lines and closed circles represent compositions without Claroideoglomus claroideum, dashed regression lines and open circles represent compositions with C. claroideum. See Methods for details. Gray area indicates ±1 s.e.
Fig 4.
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).
Fig 5.
Effects of choice between AMF.
Difference in shoot total carbon content (C), phosphorus (P) and nitrogen (N) content between choice and no-choice microcosms. Bars and error bars show means and standard errors, using species composition as unit of replication.
Fig 6.
Percent differences in 14C transferred to AMF, radio-active P (*P) transferred from AMF to plants and 14C:*P between plants and AMF when plants did and did not have a choice between AMF species.
Positive values reflect higher amounts in plants with a choice of AMF species, negative values the reverse. Error bars are ± 1 s.e. of the mean.