Parasitic plants regulate C and N distribution among common mycorrhizal networks linking host and neighboring plants

Common mycorrhizal networks (CMNs) can link multiple plants and distribute nutrients among them. However, how parasitic plants regulate the carbon and nutrient exchange between CMNs and the linked plants is unknown. Thus, we conducted a container experiment with two Trifolium pratense grown in two plastic cores and connected only by CMNs using a 25-μm nylon fabric in each container. Host T. pratense was parasitized or not parasitized by Cuscuta gronovii. CMNs were left intact or broken by rotating the cores with the host or neighboring T. pratense. The dual ¹⁵N and ¹³C labeling method was used to evaluate the N distributed by CMNs to the host and neighboring T. pratense and the recently fixed C from the host and neighboring T. pratense to CMNs. The results showed that CMNs distributed more ¹⁵N to unparasitized neighboring T. pratense than the parasitized host T. pratense. Moreover, the unparasitized neighboring T. pratense provides more recently fixed C to CMNs than the parasitized host T. pratense. These results revealed that the parasite regulated C and nutrient exchange between CMNs and the linked plants following the reciprocal rewards rule. Moreover, this study highlights the importance of parasitic plants in the regulation of mutualistic interactions in ecological webs.