Response strategies of Ochroma lagopus to short-term low-temperature stress and rewarming: a photosynthesis-antioxidant-carbon network analysis

This study investigated the dynamic responses of photosynthetic physiology, antioxidant system, osmotic regulatory substances, and carbohydrate metabolism in seedlings of the tropical tree species Ochroma lagopus Swartz under different low-temperature (3°C, 5°C, 7°C) stress for 24 h and subsequent recovery (12 h, 24 h, 48 h). The results showed that low temperatures significantly reduced chlorophyll a content and the maximum photochemical efficiency of PSII (Fv/Fm). However, carotenoids content increased by 33.97% under 5°C, enhancing photoprotection through the xanthophyll cycle. Photosynthetic parameters recovered rapidly after rewarming from 7°C, while the photosynthetic system collapsed under 3°C due to thylakoid membrane damage. In terms of antioxidant and osmotic regulation: under 3°C stress, superoxide dismutase (SOD) activity increased by 109.70% and proline (PRO) accumulated by 35.66%, alleviating damage by scavenging reactive oxygen species (ROS) and maintaining osmotic pressure. Soluble protein (SP) increased under 5°C, reflecting conservative osmotic regulation. In non-structural carbohydrate (NSCs) metabolism: starch accumulated by 23.08% under 5°C stress, and the soluble sugar/starch ratio increased by 163.99% after recovery, prioritizing energy supply for repair. Under 3°C, NSCs were depleted, blocking repair processes. PCA revealed that the core response dimension during low-temperature stress was “antioxidation - carbon allocation,” which shifted to “photosynthetic repair - energy supply” during recovery. In summary, O. lagopus adapts to low temperatures through a “three-level strategy”: efficient repair at 7°C, homeostasis maintenance at 5°C, and stress tolerance at 3°C. This study reveals the precise adaptation mechanism of tropical tree species to low temperatures, providing a theoretical basis for stress resistance management of tropical vegetation.