RESUMEN
Objective:To explore the effect of natural decay of exogenously added fibrous roots on the growth and development of <italic>Paris polyphylla</italic> var. <italic>yunnanensis </italic>and its medicinal quality. Method:The effects of natural decay of fibrous roots at different amounts on mycorrhizal infection rate， physiological and biochemical indexes， and saponin contents of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>were studied in pot culture experiments at room temperature. Result:The results showed that the infection rate of arbuscular mycorrhizal （AM） fungi in the root of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>was not significantly affected by different fibrous root treatments， but there were significant differences in infection intensity. The photosynthetic pigment content in the leaves declined significantly with the increase in fibrous root amount， and the total chlorophyll was decreased by 78.7% at most. The contents of soluble protein， soluble sugar and malondialdehyde in the leaves of <italic>P. polyphylla</italic> var. <italic>yunnanensis </italic>showed an overall upward trend. The activities of the three protective enzymes varied. The peroxidase and malondialdehyde were reduced by 181.6% and 200.0% at most. In the root system of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>， the contents of the above-mentioned six components decreased to varying degrees， with the largest reductions of peroxidase and malondialdehyde reaching 44.6% and 69.7%. Different fibrous root treatments resulted in a decrease in active component content of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>. The total content of the four saponins was decreased by 58.9% at most， and the total saponin content by 46.9%. Conclusion:The natural decay of fibrous roots affects the soil microbial environment of root system， reduces the photosynthetic pigment content in leaves， and destroys the stability of cells， thus interfering with the growth and development of <italic>P. polyphylla </italic>var. <italic>yunnanensis</italic>， reducing its medicinal components， and causing continuous cropping obstacles.