Abstract:

Objective: Litters decomposition is an important process for the material cycling and energy flow in ecosystems. The mixture of litter components will have a non-additive effect on the decomposition rate, i.e., the decomposition rate of mixed litter is higher or lower than the weighted average of the decomposition rates of all single components. The Rhododendron delavayi forests are important sightseeing resources in the Baili Azalea Forest Area in Bijie, Guizhou Province of China. The litters and humus layer of these forests exert numerous ecological services, such as soil erosion control, carbon sequestration, and water regulation.Especially, the flower has good pharmaceutical value. Collecting fresh flower litter during the flowering season is the main approach to use this pharmaceutical value. However, an urgentissue is to determine the rationalintensity of flower collection with a precondition of no obvious effect on litter decomposition so that the structure and functions of the humus layer can be maintained. In this decomposition study of the litter of R.delavayi, a dominant species of the azalea forests, the non-additive effect in the treatments with different flower-leaf ratios was quantified, a decomposition model was developed and used to simulate the decomposition response to the variation of flower-leaf ratio, and the rational intensity of flower litter collection was explored. Method: A one year field decomposition study was implemented in fixed plots with 420 mesh bags filled with mixed litter of 7 treatments. These treatments had a flower dry weight ratio of 0 (pure leaves), 10%, 20%, 30%, 40%, 50%, 100% (pure flowers). Each treatment had 60 repeats. The loss of litter mass was measured in every two months.A litter decomposition model was set up based on the Olson equation to illustrate the litter decomposition response to the flower ratio and decomposition time. Result: The remaining rate of mixed litter treatments decreased with rising decomposition time and flower ratio. For the flower ratios of 0, 10%, 20%, 30%, 40%, 50%, and 100%, the remaining rate after one year decomposition was 63.1%, 58.7%, 60.2%, 56.8%, 56.2%, 55.5%, and 55.2%. The decomposition rate in different time periods was the highest during the 0-61 days (0.054 g·d^-1), and then decreased to 0.017 g·d^-1 during the 62-183 days, then slightly increased to 0.024 g·d^-1 during the 184-306 days, but decreased to 0.005 g·d^-1 during the 70-365 days. A non-additive effect existed for the decomposition of mixed litter, and it promoted the decomposition in this study. For the treatments with the flower ratios of 10%, 20%, 30%, 40%, and 50%, the highest non-addictive effect was found to be 7.8%, 4.7%, 6.9%, 6.8%, 6.6% after the decomposition of 365, 365, 330, 310, 207 days, respectively. A litter decomposition model consideringthe non-additive effectwas well established, with a high determination coefficient of 0.987. Based on the model simulation, the highest decomposition rate after one year was 48% for the flower ratio of 80%. For the near natural flower ratio of 20% and artificially reduced flower ratios of 15%, 10%, 5%, and 0, the simulated remaining rates after one yeardecomposition were 60%, 61%, 62%, 64%, and 66%, respectively. After one year field decomposition, the mean remaining rates of the treatments with flower ratios of 10% and 20% (close to natural ratio) were 58.7% and 60%, are no significant difference between them; but both were significantly lower than that of the treatment of pure leaves. This means that when the remained flower litter ratio after the flow litter collection is not below 10%, the decomposition rate of the litter can be basically maintained at the natural level. Conclusion: The decomposition rate of the mixed flower-leaf litter of R. delavayi forests increases with rising flower ratio. The decomposition dynamics can be predicted accurately using the established decomposition model which considers the non-additive effect. The collection intensity of flower litter from the R. delavayi forests should not exceed one half of the natural flower litter for pharmaceutical use, so that the natural decomposition rate of litter and the natural structure and functions of the humus layer can be maintained.

Key words: Rhododendron delavayi, litter, flower ratio, decomposition rate, flower use