Influence of altitudinal gradients on morphological, physiological, and antioxidant enzyme activities of selected medicinal plants in the Western Himalayas

Altitudinal gradients impose climatic constraints that influence plant traits and physiological–biochemical processes, shaping adaptive responses in Himalayan ecosystems. This study assessed how altitude (940–2020 masl) affects morphological, physiological, and biochemical traits, including antioxidant enzyme activities, in Eupatorium adenophorum, Asparagus adscendens, and Berberis lycium in the Western Himalayas, Uttarakhand. The findings revealed clear species-specific functional adjustments across elevations. Plant height ranged from 133.22 ± 9.68 to 213.93 ± 6.03 cm, with the highest at lower altitudes and declining toward higher elevations. Leaf number maximized at mid-altitude (47.33 ± 26.42), followed by lower (37.89 ± 21.01) and upper elevations (29.78 ± 17.27), with similar trends observed for other leaf structural traits. Chlorophyll content increased with increasing altitude, indicating enhanced photosynthetic acclimation. However, proline content decreased with increasing altitude, ranging from 24.27 ± 6.50 to 27.45 ± 7.74 µmol g⁻¹FW. Carotenoids and total phenols were highest at mid-altitude. Antioxidant responses varied; SOD activity was highest at the upper altitude (0.073 ± 0.019 U g⁻¹, followed by the mid (0.067 ± 0.007 U g⁻¹) and the lower (0.058 ± 0.007 U g⁻¹), whereas POD activity was highest at the higher altitude (1.20 ± 0.33 U g⁻¹. DPPH radical scavenging activity peaked at low-altitude (41.11 ± 22.4 µg mL^− 1). The study indicates that plant species employ coordinated morphological, physiological, and biochemical strategies to adapt and survive at various altitudes. This research could improve our scientific understanding of plant resilience and help predict responses of Himalayan ecosystems to climate change.