Decoupling of whole-plant economic strategy from population performance in the invasive Solidago canadensis along geographic gradients in China
The whole-plant economic spectrum captures resource-use strategies along three key gradients: a conservation–acquisition gradient reflecting trade-offs in resource investment, a belowground collaboration gradient representing the continuum from ‘do-it-yourself’ to ‘outsourcing’ via mycorrhizal fungi, and a plant size gradient capturing variation in stature. However, how these axes apply to intraspecific trait variation and mediate invasion success along geographic gradients remains unclear. We measured traits, population performance, and environmental variables in the invasive forb Solidago canadensis across latitudinal and longitudinal gradients in eastern subtropical China. Populations shifted along the conservation–acquisition axis from conservative to acquisitive strategies with increasing longitude; this shift was marginally significant along latitude. Contrary to the expectation that plant size and collaboration gradients are independent, these two dimensions were coupled and showed no clear geographic trends. Environmental factors significantly influenced intraspecific trait variation, economic strategy positioning, and invasion performance. Native diversity explained the largest proportion of variation in economic strategy and performance. Crucially, we found no significant relationship between the major axes of the whole-plant economic spectrum and population performance. This suggests that diverse trait combinations may yield similar fitness outcomes, indicating fitness homeostasis across heterogeneous environments. We conclude that while geographic gradients shape whole-plant economic strategies in S. canadensis, its invasion success is likely driven by adaptive trait combinations that maintain high fitness, rather than a single optimal strategy directly mediating performance.