Comparison of Seasonally Adaptive Metabolic Response Strategies of Two Acer Species

Acer L. species are well known as ornamental trees due to their colourful leaves in autumn season. Acer pictum subsp. mono (Maxim.) H. Ohashi (APM) and Acer tataricum subsp. ginnala (Maximowicz) Wesmael (ATG) form leaves with completely different colours in autumn, yellow and red, respectively. In response to this phenomenon, we investigated the metabolic regulation of APM and ATG in different seasons by combining metabolomics, ionomics, the antioxidant system and pigment content. The results showed that the process of senescence and discolouration exists in leaves of different Acer species, and the regulatory strategy shows species specificity. Compared with green leaves, the accumulation of primary metabolites in autumn leaves of APM was extensively depleted, chlorophyll content was decreased, and antioxidant enzymes and C6C3C6 type phenolic compounds synergistically enhanced the antioxidant capacity of plants to cope with senescence. Carotenoid content was raised, which together with phenolic compounds (chlorogenic acid, rutin) provides the leaves with a yellow colour. The response of chlorophyll and the antioxidant system in autumn leaves of ATG is consistent with that of APM, while sugar content increases. The increased anthocyanin content in autumn leaves of ATG explains the transition of leaves from green to the red colour, which may be accompanied by the combined effect of elements (Fe, Zn, Mn) and isoflavones. This study provides a reference for the study of colouration mechanism and seasonal adaptation in Acer L. species.