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 facilitating the transfer/exchange of 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). InTrifolium repens , a defense signal against Mamestra brassicae larvae can be transferred to younger ramets within 35–51 h depending on genotypic variation. Induced but undamaged ramets lose their resistance after 28 days (Gómez, Van Dijk & Stuefer, 2010). Besides direct plant-plant links via plant parts, higher parasitic plants are also an important link in wired communications that enhance plant fitness.