Phenotypic and functional trait variation in Malvastrum coromandelianum under different tree plantations in Pakistan.

Malvastrum coromandelianum (L.) Garcke (Malvaceae) is a widely distributed herbaceous species known for its ecological adaptability and invasive behavior in tropical and subtropical ecosystems. In plantation forests, such invasive understory species can alter community composition, affect regeneration, and influence ecosystem functioning. Understanding their trait plasticity across contrasting tree plantation environments is critical for managing understory biodiversity and assessing the ecological consequences of afforestation practices. This study examined the phenotypic and functional responses of M. coromandelianum across different tree plantations in Pakistan, focusing on how canopy-driven microclimatic variation and soil physicochemical conditions influence its morphological, physiological, and anatomical traits. Results revealed that functional trait responses were highly variable and plantation-specific. Plant height, shoot length, and glycine betaine accumulation were highest under Morus nigra, corresponding with elevated soil phosphorus and calcium, while the longest roots and highest proline levels occurred under Melia azedarach, where soil calcium and magnesium were also enriched. The smallest individuals were observed under Tecomella undulata, where higher sodium and lower nutrient availability may have constrained growth. Ion concentrations in plant tissues varied significantly across plantation types, generally aligning with soil ion availability-for instance, elevated shoot and root sodium under Melia azedarach corresponded with higher soil salinity, while calcium accumulation was greatest in soils with higher calcium. Leaf anatomical traits, including thicker mesophyll and midrib tissues under Morus nigra, suggested resource-acquisitive strategies, while root epidermis and stem sclerenchyma thickening under Conocarpus lancifolius reflected stress-tolerant adaptations. Structural traits varied along the Leaf-Stem-Root Economics Spectrum (LSRES), indicating a balance between conservative and acquisitive strategies depending on resource availability. These findings highlight the species considerable plasticity in response to integrated canopy and soil factors. However, given its invasive nature, M. coromandelianum should not be promoted for use in ecological restoration without careful consideration of its ecological impacts. Instead, its consistent trait responses make it a potentially valuable bioindicator for assessing understory microhabitat conditions, especially in semi-arid plantations.