Photoprotective pigment plasticity and cold acclimation strategies in Cryptomeria japonica across two common gardens.

To cope with winter stress from low temperatures and excessive light, evergreen conifers employ seasonal adjustments in photosynthetic function. Understanding these regulatory mechanisms is critical for predicting coniferous forest responses to climate change and their role in the global carbon cycle. To assess variation in cold acclimation strategies, the following were analyzed: pigment composition, photochemical efficiency of photosystem II, and photosynthetic parameters in three to five provenances (Prv) of Cryptomeria japonica grown in two common gardens (CGs) with contrasting climates. All Prv exhibited winter chlorophyll reduction, increased xanthophyll cycle, lutein pigments, and rhodoxanthin accumulation, reflecting conserved photoprotective responses. However, needle chlorophyll concentrations were unexpectedly higher in the colder site, especially in the northernmost Prv, suggesting genotype-specific plasticity. Higher rhodoxanthin levels in the hotter sites indicated a trade-off between the xanthophyll cycle and rhodoxanthin-mediated protection governed by winter severity. Despite these differences, values of photochemical efficiency of photosystem II were similar among Prv within each garden, though consistently higher in the hotter garden. No significant variation in photosynthetic capacity was detected among the three Prv measured. This local adaptation is further supported by high phenotypic plasticity in pigment composition and leaf morphology. These findings highlight the diverse and flexible mechanisms by which C. japonica regulates pigment composition, enabling sustained photosynthesis across seasonal extremes, and suggest a role for both winter cold and summer heat in shaping local adaptation in this widely distributed conifer.