Does clonal integration benefit clonal plants against local allelopathic stress? Evidence from experiment of two congeneric plant pairs

Abstract Physiological integration can benefit clonal plants against many types of environmental stress. However, it remains unclear whether physiological integration can benefit clonal plants against allelopathic stress from neighboring plants and whether such an impact differs between invasive and native clonal plants. We grew two congeneric pairs of clonal plants (Hydrocotyle verticillata vs. H. sibthorpioides; Alternanthera philoxeroides vs. A. sessilis), in which the younger ramets of each fragment were subjected to allelopathic stress from Solidago canadensis while their interconnected or disconnected older ramets were not. Our results revealed that the benefits of clonal integration are highly species-specific. For Hydrocotyle species, clonal integration significantly alleviated allelopathic stress, facilitating a “tolerance strategy” (maintaining root biomass) which in turn supported an “escape strategy” (increasing creeping stems growth) in distal ramets, without imposing significant costs on donor ramets. However, for Alternanthera species, neither clonal integration nor species nativeness affected biomass accumulation. Importantly, while the invasive H. verticillata produced significantly higher total biomass than native H. sibthorpioides, this competitive advantage was driven primarily by its greater intrinsic vigor rather than higher clonal integration efficiency, although H. verticillata showed a potential tendency for optimized leaf allocation. These findings indicate that while physiological integration plays a vital role in mitigating allelopathic stress, the dominance of invasive clonal plants may stem more from their inherent growth traits rather than from superior physiological integration capabilities per se.