The 'plant killer' strategy: Nonstructural carbohydrates (NSC)-driven coordination of carbon allocation and nitrogen...

Mikania micrantha, known as the "plant killer," successfully invades forests by rapidly climbing trees and covering the canopy with extensive branching. However, the integrated above-belowground coordination mechanism that sustains this invasion remains unclear. To elucidate this mechanism, we simulated the canopy-covering process via stem bending and compared M. micrantha with two companion species (Ipomoea nil and Paederia scandens). By integrating physiological and transcriptomic analyses, we propose a mechanistic model that connects nonstructural carbohydrates (NSC) allocation, sink strength, and sugar-hormone-nitrogen signaling to coordinate shoot expansion with root nitrogen acquisition. During canopy coverage, M. micrantha exhibited higher acid invertase (AI) and neutral invertase (NI) activities than its companion vines to maintain glucose accumulation in stems, alleviating the inhibition of elongation induced by weakened apical dominance. Branches exhibited elevated cell wall invertase, AI, and NI activities and NSC accumulation, promoting rapid aboveground biomass expansion. Enhanced aboveground NSC pool promoted sucrose translocation to roots via the high expression of sucrose transporters (MmSWEET10 and MmSUC4), stimulating root carbon allocation and metabolism. Accumulated soluble sugars in roots likely activated auxin and gibberellin biosynthesis, brassinosteroid signaling, and cytokinin transport, thereby upregulating nitrate transporter genes (such as MmNPF7.3) to sustain shoot growth. This NSC-mediated carbon-nitrogen feedback reveals the invasive mechanism by which M. micrantha rapidly covers forest canopies.