Decomposition dynamics and nutrient release of litters for four artificial forests in the red soil and hilly region of subtropical China

Litter decomposition and nutrient release of four artificial forests in the subtropical, red soil and hilly region of China were examined using the litter bag method within two consecutive years in this paper. Decomposition rates and the release dynamics of carbon and nitrogen of the four forests, Pinus massoniana, Pinus elliotti, Cunninghamia lanceolata and Schima superba+Pinus massoniana were measured. The experiments were conducted in two different decomposition conditions of aboveground and belowground. The orders of litter decay rates(annual mass loss) of the four forest types for aboveground group were P.massoniana S.superba+ P.massoniana P.elliottii C.lanceolata in the first experimental year, and P.massoniana S.superba+ P.massoniana C.lanceolata P.elliottii in the second year. The litter decay rates for aboveground group were generally higher than those for belowground group in the above forests, and that for P.massoniana forest was the highest among all during the whole experimental period. Litter decomposition processes were simulated using Olson′s exponential models, which were found the best of fits to the data. According to the models, it needs 4-10 years to reach the 95% of decay rate for the investigated forests in the experimental region, and the time is between that of 8-17 years for the warm temperate forest and that of 2-8 years for the south subtropical forest. Release dynamics of nutrients differed in four forest types and also by different decomposition periods. The release rates of carbon showed a continuously increasing pattern in all the forests and those for aboveground group were higher than those for belowground group. At the earlier decomposition stage, the absolute content of nitrogen was increased in P. elliottii forest, P. massonian and the mixed forest. Among all there was the most significant nitrogen accumulation, and therefore the lowest release rate of nitrogen for litters in P. elliottii forest during the two experimental years, which was strongly influenced by the initial ratio of carbon to nitrogen for litter samples in the overhead forest. The litter samples for Cunninghamia lanceolata had the lowest C/N ratio and therefore a relatively high release rate for nitrogen during the two experimental years.