Objective  To illuminate the effects of the forest type on chemical defense of pure and mixed larch stand.

Method  Larch (Larix olgensis) forest and larch-ash (Fraxinus mandschurica) mixed forest were used as the test materials, and the activity of several defense proteins and the content of secondary metabolic compounds were tested in larch needles of different forest type.

Result  The results showed that the activity of several defense proteins and the content of secondary metabolites in larch needles of 30-year-old larch-ash mixed by strips of 4:4 (HJ30_(4:4)) and 20-year-old larch-ash mixed by strips of 4:4 (HJ20_(4:4)) significantly increased, compared with that of 30-year-old L. olgensis pure stand (CL30) and 20-year-old L. olgensis pure stand (CL20) (P < 0.05). It was found in Zhangjiawan site that the activities of polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), trypsin inhibitor (TI) and the contents of flavonoids and lignin in larch needles of HJ20_(4:4) were the highest, while the activities of PPO, PAL and the content of lignin were higher than that in larch needles of 20-year-old larch-ash mixed by strips of 2:10 (HJ20_(2:10)) (P < 0.05). In larch needles of HJ20_(2:10), the CI activity significantly increased (P < 0.05), and the tannin content added (P>0.05) in contrast to that in needles of HJ20_(4:4).

Conclusion  These results indicate that larch-ash mixed forests significantly strengthen the activity of defense proteins and increase the content of secondary metabolites in larch needles, which improve the resistance to defoliators. Compared with HJ20_(2:10), the induced defense of HJ20_(4:4) is stronger, and HJ20_(4:4) is more applicable to build the mixed forest.