Abstract: The walnut understory industry is growing rapidly. To understand the allelopathy effects of walnut leaf litter decomposition and provide a theoretical basis for the forest medicine compound planting model, we conducted a pot experiment to examine the effects of walnut litter decomposition on physiological characteristics and medicinal quality of rhizome of Paris polyphylla var.yunnanensis. There were five litter application rates, i.e. 0 (CK), 30 (H1), 60 (H2), 120 (H3), and 180 g·pot^-1 (H4). The results showed that the regulation effect of walnut leaf litter on leaf photosynthetic pigment content, rhizome fresh weight, dry weight, and dryness rate of P. polyphylla var.yunnanensis leaves followed the trend of “promoting at low concentration and suppressing at high concentration”. Compared with CK, H1 treatment had a positive effect on the growth of P. polyphylla var. yunnanensis. There was a negative effect on growth of P. polyphylla var.yunnanensis when the application amount of litter exceeded the tolerance threshold. Contents of malondialdehyde, soluble sugar, soluble protein and activities of superoxide dismutase, catalase and peroxide were gradually enhanced with increasing application amount of walnut leaf litter. The positive or negative effects of walnut leaf litter degradation increased with increasing application amount. Overall, low-dose application of walnut leaf litter can promote the growth of P. polyphylla var.yunnanensis, while high-dose application has a strong allelopathic effectby promoting oxidative damage and inhibiting chlorophyll synthesis. The planting density of walnuts should be strictly controlled in the compound planting of walnut + P. polyphylla var.yunnanensis.

Key words: walnut (Juglans regia L.), leaf litter, Paris polyphylla var.yunnanensis, allelopathy, resistant physiology, medicinal quality.