Abstract: Aims Previous studies have shown that different growing season stages and twig ages are the key factors affecting the variation of plant twig traits, however, few studies simultaneously explored the variation of twig traits and the relationship between twig traits with growing season stages and twig ages. Methods In this study, Pinus koraiensis, Picea koraiensis and Abies nephrolepis, which are typical evergreen conifers in northeast China, were studied. Seven traits including specific twig length, twig dry matter content, twig wood density, the pith proportion cross-sectional area ratio, the xylem proportion cross-sectional area ratio, the phloem proportion cross-sectional area ratio and the resin channel proportion cross-sectional area ratio of annual and perennial twigs were measured in the early growing season (July), middle growing season (September) and late growing season (November) of 135 trees. To explore the effects of different growing season stages and twig ages on twig traits and correlation among traits. Important findings In early growing season, twig dry matter content and twig wood density were significantly lower than those in middle and late growing season, while the resin channel proportion cross-sectional area ratio was significantly higher than the other two stages. The xylem proportion cross-sectional area ratio and the phloem proportion cross-sectional area ratio increased significantly with the increase of twig ages. The negative correlation between twig wood density and twig dry matter content of annual twigs was lower in early growing season. The negative correlation between specific twig length and twig dry matter content only existed in early growing season. In early growing season, annual twigs showed high specific twig length and low twig dry matter content. This proves that the early growing season of the annual twigs adopt the "quick investment - return" survival strategy. On the contrary, the late growing season and perennial twigs adopted the "slow investment-return" survival strategy. The results of this study provide insight into how plants adapt to habitat changes by regulating twig traits.

Key words: growing season stages, twig ages, twig wood density, the xylem proportion cross-sectional area ratio, the phloem proportion cross-sectional area ratio