Aims This study investigated the effects of mother tree age, low temperature stress, and their interaction on the growth and leaf physiological characteristics of Caragana korshinskii seedlings.
Methods In this study, seeds of C. korshinskii were selected from an artificial forest in the hilly and sandy area of northwest Shanxi Province, representing five mother tree ages (7, 13, 19, 41 and 51 a). These seeds were germinated, and the resulting seedlings (about 2 months) were used as test material. The low temperature stress was applied at (-8 ± 1) °C with varying stress levels: W1 (6 h), W2 (12 h), W3 (24 h), W4 (48 h) and W5 (72 h). A control group (CK) was maintained at 25 °C (normal temperature). Different growth and physiological indicators related to frost resistance were determined, and a comprehensive evaluation was conducted using the membership function method.
Important findings The results showed that: (1) There were significant differences in the impact of low temperature stress on photosynthetic pigments and osmotic adjustment substances in C. korshinskii seedlings from different mother tree ages. Notably, mother tree age and low temperature stress had significant effects on chlorophyll (Chl) a content, while the contents of Chl b, Chl (a+b), carotenoid and Chl a/b in C. korshinskii seedlings were influenced by mother tree age, low temperature stress and their interaction. Low temperature stress as well as the interaction between low temperature stress and mother tree ages, had a significant effect on soluble sugar content, while mother tree ages, low temperature stress and their interaction significantly influenced free proline content. With the increasing low temperature stress duration, the contents of Chl a, Chl b, and Chl (a+b) in the leaves of C. korshinskii seedlings initially decreased and later increased, while the Chl a/b and carotenoid content exhibited an initial increase followed by a decreased, and the content of free proline increased. (2) Low temperature stress had variable effects on the growth of C. korshinskiiseedlings from different mother tree ages. Plant height, leaf number, dry mass, main root length and root shoot ratio of seedlings germinated from seeds from different age plants displayed significant differences, with values initially increasing and then decreasing with the increase in mother tree age. However, low temperature stress significantly inhibited the plant height of the seedlings, with no significant interaction observed between mother tree age and low temperature stress on the aforementioned growth parameters. (3) Seedlings germinated from the seeds of young mothers (7, 13 a) showed stronger frost resistance than those from older mothers (19, 41, 51 a). In summary, physiological parameters including Chl b content, Chl (a+b) content, Chl a/b, carotenoid content and growth parameters such as plant height, leaf number, dry mass, main root length and root shoot ratio can serve as indicators for assessing frost resistance in C. korshinskii seedlings. Besides that, when promoting the natural regeneration of C. korshinskii forest through artificial means, selecting seeds from young and middle-aged C. korshinskii plants can enhance the success of regeneration.