Fine root decomposition characteristics of Pinus massoniana Lamb. and Camellia oleifera Abel. under P. massoniana forest

【Objective】To explore decomposition characteristics and nutrient dynamics of single and mixed fine roots of Pinus massoniana Lamb. and Camellia oleifera Abel.，and to reveal the interaction mechanism between them，so as to provide theoretical reference for the compound management and efficient cultivation of P. massoniana plantation. 【Method】Fine roots of P. massoniana and C. oleifera in aerially seeded P. massoniana forest were collected. The change of dry mass residual rate of P. massoniana and C. oleifera and the dynamics of carbon（C），nitrogen（N），phosphorus （P），patassium（K），calcium（Ca）and magnesium（Mg）elements in one year were measured by in situ decomposition bag method，and the mixed effect of fine root decomposition was analyzed.【Result】The initial C content，Ca content，C∶N， C∶P and N∶P of fine roots of P. massoniana were significantly higher than those of C. oleifera（P<0.05，the same below）， while the contents of N，P，K and Mg were significantly lower than those of C. oleifera. There were two stages in fine roots decomposition process：fast decomposition and slow decomposition. The elements C，P，K and Mg in fine roots showed net release overall，while Ca showed enrichment；N in C. oleifera showed net release，and P. massoniana enrichment. During the one-year decomposition，the nutrient release rates of P. massoniana fine roots was K>C>Mg>P，and the nutrient release rate of C. oleifera fine roots was K>Mg>P>C. The release rate of N，P，K and Mg in C. oleifera fine roots was significantly higher than that of P. massoniana fine roots，while the Ca enrichment was lower in C. oleifera fine roots than that in P. massoniana fine roots. The mixed treatment of P. massoniana and C. oleifera fine roots inhibited fine roots decomposition in the early stage of decomposition（0-3 months），and promoted decomposition in the later stage（9-12 months），showing a complex impact on nutrient elements. The mixed treatment significantly inhibited the release of N and K elements in fine roots，inhibited the accumulation of Ca in the early stage of decomposition，promoted Ca accumulation in the 6-9 months，and both promoted and inhibited the release of C，P and Mg. The fine roots decomposition rate was significantly positively and negatively correlated with temperature and humidity，respectively.【Conclusion】The mixing of P. massoniana and C. oleifera has different effects on the decomposition of fine roots and nutrient release of litters. The mixing of fine roots of both species significantly promotes fine roots decomposition in the late decomposition period，and the mixing effects significantly inhibits the release of N element in fine roots. Therefore，the economic benefits of mixed tree species and the mixing effects of litters should be considered in the production.