Aphid herbivory drives asymmetry in carbon for nutrient exchange between plants and an arbuscular mycorrhizal fungus

Study conducted to investigate the effect of manipulating the source and sink strengths of plant C resources on carbon for nutrient (P) exchange between wheat and an arbucular mycorrhizal fungus. C source strength was manipulated by growing plants at ambient and elevated atmospheric [CO2]. C sink strength was manipulated by the addition or exclusion of Rhopalosiphum padi aphids.
Our research questions were as follows:
(i) Does increasing external C sink strength (i.e. addition of aphids) reduce plant C allocation to an AM fungus?
(ii) Does increasing C source strength (i.e. elevated [CO2]) increase plant C allocation to an AM fungus?
(iii) Can increasing C source strength mitigate increased external plant C sinks?
(iv) Does plant assimilation of mycorrhizal-acquired nutrients change relative to plant C allocation?