| The leaf litter is an important part of forest carbon pools, and its cycling speed directly impact on the carbon cycle of forest ecosystems, thereby affecting the whole forest ecosystem carbon budget. Therefore, the decomposition of forest leaf litter and carbon dynamics study is particularly important. In order to study the leaf litter decomposition rates and carbon dynamics, the experiment use litter bags, and select nine tree species of tropical and subtropical China, these tree species including Phyllostachys heterocycla, Schima superba, Cyclobalanopsis glauca, Cunninghamia lanceolata, Pinus massoniana, Metasequoia glyptostroboides, Cycas revolute, Alsophila spinulosa, Dicranopteris dichotoma. The experiment time is 840d, and the decomposition experiment of leaf litter in three sites (Qiandaohu in Zhejiang Province, Dinghushan in Guangdong Province, and in Jianfengling in Hainan Province) were conducted along with climate gradient. The sites represented the mid-subtropical area, southern-subtropical area, and tropic area. The experiment uses the condition of Dinghushan to simulate the situation of temperature rising 4℃in the future, and simulate the temperature rising 6℃in the future using Jianfengling.The experiment aimed at studying the leaf litter decomposition of the tree species in subtropical response to global warming and the impact of the carbon cycle.The results indicated that: (1) The order of leaf litter is Phyllostachys heterocycla> Cyclobalanopsis glauca > Schima superb > Pinus massoniana > Cunninghamia lanceolata > Metasequoia glyptostroboides > Alsophila spinulosa > Cycas revoluta > Dicranopteris dichotoma in Qiandaohu. 95% decomposition time of leaf litter range between 5.45a and 24.96a, half decomposition time range between 1.26a and 5.78a. The decomposition rate of Phyllostachys heterocycla was the fastest, the 95% decomposition time was 5.45a, half decomposition time was 1.26a. And the decomposition of Dicranopteris dichotoma is the slowest, the 95% decomposition time was 24.96a, half decomposition time was 5.78a. Annual decomposition rate (k) of leaf litter of plant taxa with different origin time is monocotyledons>dicotyledons>gymnosperms>pteridophyta. The decomposition of leaf litter of different plant taxa was similar, and the earlier the origin time, the slower decomposition. And significant difference (p<0.05) was found for litter decomposition rates in monocotyledons, gymnosperms and pteridophyta, but there was no significant difference in dicotyledons and monocotyledons, dicotyledons and gymnosperms.(2) The order of leaf litter is Phyllostachys heterocycla> Cyclobalanopsis glauca > Schima superb > Pinus massoniana > Cunninghamia lanceolata > Metasequoia glyptostroboides > Cycas revoluta > Alsophila spinulosa > Dicranopteris dichotoma in Dinghushan. 95% decomposition time of leaf litter range between 4.22a and 21.40a, half decomposition time range between 0.98a and 4.95a. The order of leaf litter is Phyllostachys heterocycla> Schima superb > Cyclobalanopsis glauca > Pinus massoniana > Cunninghamia lanceolata > Metasequoia glyptostroboides > Cycas revoluta > Alsophila spinulosa > Dicranopteris dichotoma in Jianfengling. 95% decomposition time of leaf litter range between 3.79a and 12.48a, half decomposition time range between 0.88a and 2.89a. Annual decomposition rate (k) of leaf litter of plant taxa with different origin time is monocotyledons>dicotyledons > gymnosperms > pteridophyta. If the future temperature rise 4℃, the 95% decomposition time of monocotyledons, dicotyledons, gymnosperms and pteridophyta will shorten 22.57%, 14.78%, 18.73% and 20.75%. But if the temperature rise 5.9℃, the time will shorten 30.46%, 27.23%, 26.16% and 39.71%. It indicated that if the climate warming in the future, the litter decomposition rate will accelerate along with the temperature rising, and the sooner the origin of plant litter, the greater the response to the global warming.(3)The carbon density and the amount of total carbon have a downward trend in three sites, and most of the species appears two rising process in the decomposition process, the time of occurrence concentrated in January,2007 (winter) and March 2008, the late increase in magnitude much smaller than the previous. It indicated that the leaf litter decomposition is slower in the winter, carbon appeared accumulation, the accumulation rate decreases in the latter part of decomposition. In March 2008, carbon appears accumulation, speculating that the lower temperature because of the snow calamity in southern China.(4)The order of carbon release is dicotyledons>monocotyledons>gymnosperms>pteridophyta. If the future temperature rise 4℃, carbon release of leaf litter of different plant taxa were not pronounced. If the future temperature rise 5.9℃, carbon release of leaf litter of different plant taxa were increased greatly. Pteridophyta is most obvious, increased 19.11%, gymnosperms increased 8.68%, dicotyledons increased 5.28% and monocotyledons increased 1.51%. Keywords:sub-tropical area, leaf litter, decomposition, Carbon cycle, Global Change.
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