Abstract:To explore the effects of leaves loss on the growth, fruit yield, quality and related physiological characteristics of Rosa roxburghii Tratt. To provide a scientific basis for the determination of reasonable leaves collection amount and the loss assessment after the leaves loss disaster of R. roxburghii. In this study, three-year-old "Guinong 5" R. roxburghii were used as the materials in 2017. Before the flowering period in early May of the same year, the experimental trees were treated with manual leaves loss which rated of 20%, 40%, 60% and 80% of the spring shoots of the same year, and the plants without leaves loss were used as control (CK). The effects of different leaves loss amounts on the growth, leaf nutrient content, fruit yield and quality of new shoots of R. roxburghii in three years were studied. The contents of endogenous hormones, Pn and Tr of the leaves losing spring shoot within 30 days after leaves loss were measured. The activity of GalLDH, MDHAR, DHAR, AAO, APX, PAL, C4H, 4CL and CHS of R. roxburghii fruit as well as their relationship with the content of AsA and total flavonoids in the year of leaves loss were analyzed.The results showed that: the loss of R. roxburghii leaves in spring could promote the germination of summer shoots of the same year, increase the number of summer shoots, and inhibit the growth of new shoots in autumn of the same year, following year and the third year. Within 30 days after leaves loss, the contents of IAA and ABA of spring shoot after leaves loss decreased rapidly, while the contents of GA1+3 and ZR increased rapidly. The changes of endogenous hormone contents had a synergistic promoting effect on the germination of the summer shoots in the same year. The remaining leaves of the spring shoots after leaves loss had an obvious short-term photosynthetic compensation reaction. The Pn of the remaining leaves of the spring shoots increased rapidly within 15 days after leaves loss, then decreased rapidly, and the photosynthetic compensation reaction could not be sustained in the long term. The Tr of the remaining leaves of the spring shoots after leaves loss increased significantly, while the WUE decreased significantly. The leaves loss of spring shoots would lead to the nutrient loss of R. roxburghii and the decrease of nutrient elements content in leaves, especially the loss of N, P, K and Mg were serious. The leaves loss of spring shoot would seriously reduce the fruit yield and quality of R. roxburghii. With the increase of leaves loss rate of spring shoot, fruit yield and quality decreased obviously. In the critical period of the synthesis and accumulation of AsA and flavonoids in R. roxburghii fruits, the activities of GalLDH, which had an important effect on the synthesis and accumulation of AsA in R. roxburghii fruits, and the activities of PAL, C4H, 4CL and CHS, which were metabolized by flavonoids, were significantly decreased with the increase of leaves loss. The contents of AsA and flavonoids in R. roxburghii fruits also decreased significantly with the increase of leaves loss. Leaves loss which more than 20% would cause a large loss of nutrients in R. roxburghii tree, weaken the tree potential, inhibit the growth of R. roxburghii, and reduce the yield and quality of R. roxburghii fruit, and this adverse effect could last for many years. When the young leaves of R. roxburghii are harvested for use in spring, the amount of leaves collected should be controlled within 20%.