Comparative Ionomics of Lycopodiaceae and Selaginellaceae Across Diverse Soil Types in Japan

ABSTRACT Lycophytes, one of the earliest‐diverging vascular plant lineages, occur in diverse and often extreme environments, yet their ecological adaptation strategies remain poorly understood. Ionomics, characterized by elemental composition, offers insights into how evolutionary history and environmental conditions shape plant function. Here, we investigated how lineage and soil type influence ionomic profiles in terrestrial lycophytes by analyzing shoot elemental concentrations in three Lycopodiaceae species and four Selaginellaceae species collected across Japan, including serpentine soils and solfatara fields. Element concentrations were quantified by inductively coupled plasma mass spectrometry, with nitrogen and phosphorus measured colorimetrically. Statistical analyses included heatmap clustering and principal component analysis. Across non‐solfatara environments, Lycopodiaceae and Selaginellaceae showed distinct ionomic profiles at the family level within the sampled taxa, with variation appearing to be more strongly affected by lineage differences than by living environment. In Selaginellaceae, individuals from serpentine soils showed higher magnesium, iron, and arsenic, reflecting serpentine soil characteristics. Lycopodiaceae showed higher aluminum, copper, potassium, rubidium, and manganese, whereas Selaginellaceae had higher calcium, magnesium, phosphorus, nitrogen, strontium, and zinc. For Palhinhaea cernua (Lycopodiaceae), which occurred in both solfatara and non‐solfatara fields, shoots from the acidic solfatara environment contained higher sulfur, nitrogen, and phosphorus while maintaining consistently high aluminum concentrations, supporting its status as an aluminum hyperaccumulator. Overall, lycophytes demonstrate family‐specific elemental homeostasis that is conserved across environments, alongside characteristic shifts in extreme soils. These findings provide a foundation for understanding ecological diversification in the earliest‐diverging vascular plants and highlight ionomics as an effective approach for exploring their environmental adaptation strategies.