Clonal variation in drought tolerance-related traits and their association with field performance in juvenile Japanese cedar (Cryptomeria japonica)

The future survival and growth of Japanese cedar ( Cryptomeria japonica (L.f.) D. Don), a major forestry species in Japan, may be significantly affected by increases in drought intensity and frequency associated with global climate change. Understanding intraspecific variation in drought tolerance is therefore important for future forest management and breeding strategies. We hypothesized that physiological and morphological traits related to drought tolerance differ among clones and are associated with differences in growth and survival observed in long-term field trials. Second-year rooted cuttings of 15 plus tree clones of C. japonica derived from different provenances in western Japan were subjected to well-watered and drought treatments. Physiological traits, including gas exchange, carbon isotope discrimination, and osmotic adjustment, and morphological traits such as growth, biomass allocation, and growth phenology, were evaluated. Significant clonal variation was observed in most traits. Variation in stomatal conductance, photosynthetic rate, and stem growth was pronounced under the well-watered treatment, but less pronounced under the drought treatment, whereas osmotic adjustment showed greater clonal variation under the drought treatment. Drought tolerance, as assessed using principal component analysis, varied considerably among clones and was significantly associated with growth plasticity at the juvenile stage. Moreover, juvenile drought tolerance was more closely associated with long-term survival than with growth performance under field conditions. These findings provide fundamental insights for selecting drought-tolerant planting materials for C. japonica afforestation and for developing breeding strategies to enhance adaptation to future climate change.