Provenance-Specific Photosynthetic Regulation and Recovery Mechanisms of Phoebe bournei Under Chilling Stress

Cold sensitivity restricts the natural distribution of subtropical evergreen trees. In a representative species such as Phoebe bournei, evaluating physiological divergence among provenances is therefore essential for identifying cold-hardy germplasm and understanding adaptive evolution. This study investigated the photosynthetic capacity, redox homeostasis, and carbon metabolism of saplings from three provenances (WY, AF, and SC) under chilling stress and subsequent recovery. The results showed that low temperature significantly inhibited the net photosynthetic rate and photochemical efficiency in all saplings through predominant non-stomatal limitations. The northern provenance WY prioritized structural integrity and redox homeostasis by enhancing cyclic electron flow and timely antioxidant activation. The mid-latitude provenance AF demonstrated higher physiological plasticity and achieved more rapid recovery of photosynthetic activity upon rewarming. In contrast, the southern provenance SC was highly sensitive to chilling stress, exhibiting disrupted energy dissipation, severe lipid peroxidation, and impaired coordination of carbon metabolism and hormonal regulation. Overall, the pronounced divergence in adaptive strategies among provenances is evident. These findings provide a physiological basis for understanding intraspecific variation in P. bournei and offer guidance for germplasm selection under climate change.