Results/Conclusions: Clonal integration had positive effects on the performances and fitness of clonal plants by increasing photosynthetic ability, canopy growth and spatial expansion (e.g. total expansion distance and spacer length). Its contribution was greater under heterogeneous patchiness than under homogeneous patchiness, but did not differ between stoloniferous and rhizomatous clonal forms. Under spacer severing treatment, aboveground biomass decreased more in recipient ramets than in donor ramets, while belowground biomass decreased more in donor ramets than in recipient ramets. The values of the allometric exponent (a) between below- and above-ground parts (M belowground vs. M aboveground) were significantly higher under non-severing conditions than under severing conditions in donor ramets. Biomass allocation analysis showed that clonal integration enhanced the growth and/or expansion ability of recipient ramets at the cost of donor ramets. Moreover, more biomass was allocated to spatial expansion (higher spacer biomass) than to canopy growth (lower leaf biomass) under clonal integration. Clonal integration improves the performance and fitness of clonal plants partly by increasing photosynthetic capacity and canopy growth at the whole-plant level, but more importantly by altering biomass allocation and enhancing the spatial expansion ability of recipient ramets. Spatial expansion is a main strategy of clonal plants to ameliorate their performance and fitness.
