Differences in fruit yields and essential oil contents and composition among natural provenances of Litsea cubeba in China and their relationships with main habitat factors

Litsea cubeba (Lour.) Pers. is an important industrial tree in southern China and Southeast Asia. We surveyed and sampled wild L. cubeba in 32 provenances spread across nine provinces of China. We used nested variance analysis, multiple comparisons analysis, hierarchical clustering analysis, Pearson's correlation analysis, path analysis with multiple stepwise regression, detrended correspondence analysis, redundancy analysis, and variance partitioning analysis to evaluate the phenotypic diversity of fresh fruit yield (FFY) and essential oil (EO) characteristics of L. cubeba, and to explore the relationship between the main habitat factors and phenotypic diversity. We detected wide phenotypic diversity in FFY, EO content (EOC), citral yield (CitrY), and the proportions of the seven main components of EOs (citral, D-limonene, 3,7-dimethyl-3,6-octadienal, 4-methyl-3-pentenal, linalool, citronellal, and 1-(cyclopanecarbonyl)piperidin-4-one). The variation was mainly derived from among provenances (P ≤ 0.01) rather than within provenances, and the variation in FFY and CitrY was greater than that of EOC and the seven dominant components among provenances. We also detected several region-specific components of EOs in fresh fruit, including α-terpineol, geraniol, eucalyptol, and 7-methyl-3-methyleneoct-6-enal. Most of the provenances with higher FFY were distributed in southwestern China (lower longitude and latitude, and higher elevation), while most of those with higher EOC were distributed in southeastern China (higher longitude and latitude, and lower elevation). The three provenances with excellent FFY were YN-XC, GZ-ZY, and SC-KJ; the two with higher EOC were SC-KJ and HN-DX; and CitrP was higher in GZ-ZF than in other provenances. Longitude, total potassium content (TotalKC), and bulk density (BD) were the most important factors that influenced FFY diversity, while latitude, elevation, annual average relative humidity (AARH), and organic carbon content (OCC) most strongly influenced EOC diversity, and annual average temperature and annual average maximum temperature (AAMaxT) influenced CitrP diversity. The six main habitat factors together explaining the largest proportions of phenotypic diversity were longitude, AARH, AAMaxT, elevation, latitude, and soil total phosphorus content (TotalPC). Higher soil TotalKC, BD, and TotalPC were suitable conditions for cultivation of L. cubeba to achieve higher FFY, while lower AARH and OCC were favorable for accumulation of EOs, and only lower temperature was more likely conducive to citral synthesis. The wide diversity of FFY and EO characteristics should be taken into account when selecting germplasms for protection and utilization, and the identification of the most important environmental factors affecting phenotypic diversity provides a theoretical basis for the optimization of L. cubeba cultivation.