The rapid conversion of natural broadleaved forests to plantations (of mainly Cunninghamia lanceolata and Pinus massoniana) in subtropical China has resulted in a substantial decline in soil fertility, but the biogeochemical mechanism behind this decline remains unclear. Litterfall is an important source of nutrients that are returned to soils through litter deposition and decomposition. We assessed various types of litterfall (leaves, twigs, flowers, fruits and unidentified litter) and their carbon, nitrogen, phosphorus and potassium inputs to soils in a natural broadleaved forest (Castanopsis carlesii) and in P. massoniana and C. lanceolata plantations over 10 years. The total litterfall was 21-25% lower in plantations than in the C. carlesii forest, resulting in much lower carbon, nitrogen, phosphorus and potassium inputs from litterfall in the plantations. Nitrogen inputs from litterfall in the P. massoniana and C. lanceolata plantations were only 38% and 48% of that in the C. carlesii forest, respectively. Leaves accounted for 72-76% of total litterfall, so we compiled available data on the nutrient release from the three foliar litters during the 1st year of decomposition throughout subtropical China. Decomposition rates of P. massoniana and C. lanceolata needle litter were only half that of C. carlesii leaf litter, and the lower initial quality of P. massoniana and C. lanceolata needle litter relative to C. carlesii leaf litter resulted in significantly lower amounts of nitrogen and phosphorus being released. These results suggest that low nutrient inputs due to low litter production and low nutrient release due to slow litter decomposition are important biogeochemical mechanisms behind the decline in soil fertility in subtropical plantations.
 

litterfall,litter decomposition,nutrient release,forest plantation,soil organic carbon,subtropical forest