Fatty acid composition and secondary metabolites of cypress monoculture were differently influenced by neighboring species identity

Mixed forests are highly recommended for new afforestation and the transformation of vulnerable monocultures. Previous studies have shown that species mixing had strong effects on forest soil characteristics and tree growth, highly depending on the introduced species identity. However, our knowledge about the effects of neighboring species on plant metabolism is still limited. In the present study, we compared the physiological parameters and metabolome of cypress trees from a pure cypress forest (PC) and its transformed mixtures by admixing with either evergreen camphor (CC) or deciduous N 2 fixer alder (AC). In the vicinity of camphor, in addition to less negative leaf ẟ 13 C, concentrations of sucrose, polyols, fatty acids, as well as secondary compounds of phenolics and sterols were largely increased in leaves at the expense of their abundances in the roots. In contrast, concentrations of these compounds in leaves and roots both largely decreased when the neighbors were alder trees. The latter also improved leaf water content of cypress trees. Concentrations of terpenoids were generally less abundant in trees from the two mixtures in comparison to the monoculture. Trees in the CC mixture invest more in defense compounds, while trees in the AC mixture tend to invest more carbon to growth. Our findings underline that tree species mixing has strong effects on the abundances of metabolites in the leaves and roots, particularly the fatty acids and secondary metabolites in response to neighbors with distinct identities. Our study also provides valuable information for forest management in terms of specific perspectives. • Admixing strongly affects tree metabolism in a species-specific manner. • First report of the effects of neighboring tree species on fatty acid composition. • Species mixing mediate carbon allocation between growth and defense. • Admixing regulates metabolism and allocation between leaves and roots.