Local Adaptation and Edaphic Divergence Across Ultramafic and Non‐Ultramafic Soils: Insights From Artificially Controlled Experiments and Elemental Profiles

ABSTRACT Ecological speciation is a continuous process driven by divergent selection. In the early phases of speciation, local adaptation plays a significant role in enabling organisms to colonize new environments. Ultramafic environments impose strong edaphic stress on plants and lead to local adaptation and ecotype emergence. Solidago virgaurea harbors distinct ecotypes occurring on adjacent ultramafic and non‐ultramafic soils. Previous studies have employed reciprocal transplant experiments in nature to evaluate local adaptation driven by multiple environmental factors. However, the extent to which soil conditions alone contribute to ecological divergence remains unclear. Additionally, our understanding of ecotypic variation in tolerance under harsh soil conditions remains insufficient. In this study, we conducted reciprocal transplant experiments in a controlled growth chamber to isolate the effects of contrasting soil environments on plant performance. Our results showed that some ecotypic traits exhibited higher performance in their native habitat than in the alternative soil; however, the signals of local adaptation observed in field experiments were not fully reproduced. Comparative analyses of soil and plant ionomic profiles revealed ecotypic differences in functional traits related to major nutrient elements, whereas little divergence was detected in heavy‐metal profiles. These findings indicate that soil factors alone do not necessarily account for local adaptation. Nonetheless, soil chemical profiles, especially those of major nutrient elements, may play a key role in the differentiation of functional ecotypic traits. Further investigation is expected to reveal the genetic mechanisms underlying these physiological functions, and greater emphasis should be placed on environmental factors other than soil as well.