| Carbon element is not only the important component of the plant, but also one of the most active environmental factors. As the researches on the global warming advanced, the forestland soil carbon attracts great attention for its huge storage. Chinese fir (Cunninghanaa lannceolata) is a fast-growing native Chinese species with valuable timber attributes in subtropical area of southern China. The statistics form the 5th National Forest Researches Inventory showed that the total area and stocking volume of Chinese fir plantations have reached 12.39 million ha and 473.57 million m3, respectively, accounting for 26.55% and 46.89% of those of plantation in the whole nation. Chinese fir plantation has become one of the main forests in southern area, and played a role on the carbon balance of terrestrial ecosystem. To figure out the forming procedure of soil carbon storage and its balance in Chinese fir plantation, the soil organic carbon storage, litterfall amount and its decomposition, and soil respiration were studied in this dissertation. The main results of the research are as follows.The soil carbon storage in Chinese fir plantation was 126.168 t hm"2 at the depth between 0 and 75cm. In contrast to the massoniana pine forestland and the second broadleaf forestland, the carbon storage order ranked as follow: Chinese fir forestland>Massoniana Pine forestland>the second broadleaf forestlands, and they followed the same laws: soil carbon storage of different forestlands decreased as the depth of soil increased. The soil carbon storage mainly distributed in the soil surface layer (0~30cm), accounting for 53.62%, 60.02% and 64.33% of the total soil carbon storage in Chinese fir forestland, Massoniana Pine forestland and the second broadleaf forestlands, respectively.The mean annual amount of dry litter was 1201.24 kg hm-2 a-1 in Chinese fir plantation, consisting of needle leaf, fallen twig, fallen fruit and other detritus, of which the needle leaf was the largest component, the amount was 838.92 kg hm-2 a-1 and made up 69.84%. The return carbon amount through litter in Chinese fir plantation was 557.06 kg hm-2 a-1, and increased with the growth of the Chinese fir plantation. The carbon storage in litter mainly focused on the needle leaf and fallen twigs, which accounted for 94.4%. The carbon concentration of the litter varied with the components of litter-fall, the order was as follow: needle leaf > fallen fruit > other detritus > fallen twig. The annual carbon release was 158.06 kg hm-2 a-1 in the course of the litter decomposition, making up 28.25% of the carbon amount in litter. Some of themreturned to the atmosphere as CO2, and the other stored as the humus in the soil, which was one of the sources of the soil carbon. The three kinds of treatment to the needle leaf was positive to the decomposition in the experiments of the litter decomposition, the dry weight release percentage ranged from 29.13% to 43.67%, among them the understorey leaf's contribution to the decomposition of needle leaf was most great.The daily changes of soil respiration was as follows: in July, the mean soil respiration rate was 1.174 umol m-2 s-1, and the soil respiration curve over the time was two peaks, occurring at 8:00 and 16:00, which was 1.317 and 1.357, respectively; in October, the soil respiration curve over the time was single peak, occurring at 8:00 and 16:00, which was 0.984, and it changed little, ranging from 0.746 to 0.984; in December, the mean soil respiration rate was only 0.271 umol m-2 s-1, and the soil respiration curve over the time was single peak, the soil respiration reached the highest point at 18:00, which was 0.313. The soil respiration rate over season changes decreased from July to December, the mean soil respiration ranged from 0.271 to 1.174. The annual soil CO2 release amount was 10.474 t hm-2 a-1, and 2.8565 t hm-2 a-1 when it was transformed to carbon.
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