Divergent strategies of northern versus southern tree species in coping with cold stress during dormancy and budburst

Zhejiang A&F University, State Key Laboratory for Development and Utilization of Forest Food Resources, Hangzhou, China

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Cold damage is a significant natural factor affecting plant growth and distribution. It is particularly important at spring budburst stage, when plants undergo marked changes in cold hardiness. Global climate change has led to frequent extreme low-temperature events, exacerbating the risk of cold damage. Earlier research has predominantly focused on single tree species or single phenological stages, lacking systematic comparisons of cold hardiness among tree species across latitudes during key phenological stages. China encompasses tropical, subtropical, warm temperate, mid-temperate, and cold temperate climatic zones. Significant climatic differences exist across this latitudinal range, resulting in varying degrees of cold damage and substantial morphological and physiological variation among plant traits across regions. We analysed systematically differences in cold hardiness across three developmental stages (dormant bud, bud swelling, fully expanded leaves) between 25 typical tree species from five climatic zones, ranging from latitude 43°20' in the north to latitude 23°15' in the south. The cold hardiness (LT₅₀) was determined using the electrolyte leakage method and observations of mortality. The dependence of cold hardiness on latitude and phenological stage was examined by logistic regression. Furthermore, we explored the physiological and ecological mechanisms underlying cold hardiness by examining changes in dormancy depth, concentrations of osmotic substances (soluble sugars, soluble proteins), antioxidant enzyme activities (SOD, POD), concentrations of endogenous hormones (gibberellin, abscisic acid), and morphological structural indicators (leaf thickness, specific leaf area, etc.) The existing results indicate that northern tree species exhibit greater tolerance to cold hardness before and at the stage of bud burst compared to southern species, along with higher soluble sugar and protein contents as well as enhanced antioxidant enzyme activity. The results provide a theoretical basis for forest tree breeding for cold hardiness, cultivation zoning, and cold damage early warning, thus enhancing forest production under changing climatic conditions.