2.1  Wired connections between clonal plants via rhizomes and stolons
Some plants produce genetically identical but independent plants (clones) through specific organs such as rhizome and stolon (Bittebiere, Benot & Mony, 2020, Vannier, Mony, Bittebiere, Theis, Rosenberg & Vandenkoornhuyse, 2019). These clonal plants are two functionally independent plants that share vascular connections and physiological integration. Clones have similar microbiomes, and represent unique models in plant–plant interaction studies (Vannier et al. , 2019). Clones communicate and enhance each other’s survival during biotic/abiotic stress (Karban, Wetzel, Shiojiri, Ishizaki, Ramirez & Blande, 2014, Qian, Li, Han & Sun, 2010, Semchenko, John & Hutchings, 2007).
Physical connections via stolon and rhizome can mitigate abiotic stress by transferring/exchanging nutrients and metabolites, or by modulating resource use efficiency (Figure 1) (Roiloa, Antelo & Retuerto, 2014). Defense signals can be transferred via phloem from older to younger ramets to induce systemic resistance in young ramets. Older ramets do not receive defense signals from younger clones due to the direction of source-sink gradient flow (Gómez & Stuefer, 2006). In Trifolium repens , a defense signal against Mamestra brassicae larvae can be transferred to younger ramets within 35–51 h depending genotypic variation. Induced but undamaged ramets lost their resistance after 28 days (Gómez, Van Dijk & Stuefer, 2010). Besides direct linked plant-plant via plant part, the higher parasitic plants also have an important role in wired communication to enhance plant fitness.