Functional role of leaf pubescence in Phacelia secunda from high elevations in the Andes of Central Chile

Leaf pubescence provides multiple protective functions against herbivores, water loss, and high irradiance in alpine plants, but how does it prevent photoinhibition when plants face simultaneous high radiation and low temperatures remain unclear. We investigated how leaf pubescence affects photosynthetic efficiency, thermal regulation, and photoprotective pigments in Phacelia secunda (Boraginaceae) across an elevational gradient in the Andes of Central Chile. We experimentally manipulated pubescence (intact vs. reduced with a razor blade) in plants collected from contrasting elevations (2100 and 3600 m a.s.l.) and exposed them to different temperatures (4 °C and 15 °C) and light regimes (40 to 1660 µmol m^-2s^- 1 PAR) to assess photochemical efficiency (Fv/Fm, φ PSII), non-photochemical quenching (NPQ), leaf temperature, and xanthophyll cycle pigments. Pubescence removal reduced photochemical efficiency at 4 and 15 °C compared to plants with intact pubescence. Additionally, pubescence removal increased the dissipation of excess energy via non-photochemical quenching (NPQf and NPQs), particularly in high-elevation plants, suggesting a compensatory mechanism to prevent photodamage. Thermal imaging revealed that pubescence promoted thermal decoupling from ambient temperature, buffering leaves against extreme fluctuations at high altitude. Despite elevated photoprotective pigments (lutein, neoxanthin) in plants with reduced pubescence, this biochemical compensation did not prevent photodamage. Leaf pubescence is a crucial trait in P. secunda, providing critical photoprotection by reducing radiation load, buffering thermal extremes, and reducing reliance on energetically costly biochemical defenses. These findings reveal how morphological adaptations buffer alpine plants against multiple environmental stresses, informing predictions of plant responses to climate change in mountain ecosystems.