Influence Of Regeneration Patterns On The Soil Organic Carbon Quality And The Soil Respiration Of Chinese Fir Plantation

The global change resulted from human activities, especially the sharp rise in CO₂ concentration and the following warming effect, have caused a widespread concern. Carbon pool maintain by the forest ecosystems covered 46.3% of the global carbon pool. Whereas continual releasing of CO₂ with the declining of the forest ecosystem carbon storage was caused by the conversion of forest with human activities. It was reported that 87% of the atmospheric CO₂ emissions had come from the global land use change during the last 150 years. Soil organic carbon storage of global 1 m soil layer is about three times of the terrestrial vegetation carbon storage, two times of the atmospheric carbon pool. Since forest ecosystems soil carbon pool covered 73% of the global soil carbon pool, its changes had been considered the main reasons of the changes of the Atmospheric carbon pool and the global climate. Affecting by land-use, environmental and man-made factors, forest carbon sequestration had showed great spatial heterogeneity and uncertainty, therefore it would be rather difficult to acquaint its effects on carbon due to forest management and update.Chinese fir, as a unique fast-growing fine and native timber tree in subtropical regions of China, accounts for 26.55% of plantation in China. Regeneration methods through controlled burning in large area after overcutting of Chinese fir plantation is one of the main forestry measures in the southern collective forest zone. There existed certain difference of the SOC and soil respiration situation through different cutting and renewal measure. The impact of different regeneration methods on the soil organic carbon and soil respiration is still unclear. In view of this situation, background chosen in subtropical area which was nearly consistent, 68-year-old aged Chinese fir plantation which had stronger comparability, 15-year-old second-rotation Chinese fir plantations through artificial regeneration which was built on the partial overcutting forestland 15 years ago (planting trees on the base of refiningmountain after overcutting ) and 15-year-old Chinese fir and broadleaved mixed forest through natural regeneration by no planting (overcutting without refmingmountain) were chosen as research objects. This paper systematically researched the differences of soil carbon storage, inconstant soil organic carbon contents, soil respiration and differences among the components of soil respiration in the forest land by different regeneration patterns. The effect of the regeneration methods in subtropical regions on the soil organic carbon and soil respiration was also discussed to provide scientific basis for the reasonable adjustment of forest management methods in subtropical regions and enhancement of carbon sink ability. The major results were summarized as follows:(1) Different regeneration patterns affected the contents of soil organic carbon. Cutting and regeneration in aged Chinese fir decreased the contents of soil organic carbon both in artificial regeneration forest and natural regenerated forest, and both of them were significantly different with the aged Chinese fir (P<0.05). For these two forests of different regeneration patterns, contents of SOC in natural regenerated forest was higher than that in artificial regeneration forest, but there was no significant difference between them (P>0.05).(2) Different regeneration patterns affected and decreased forest SOC storage. Compared with the aged Chinese fir, SOC storage in 0-100 cm layer decreased by 7.09% and 13.27% respectively in natural regenerated forest and artificial regeneration forest, and the differences were both significant (P<0.05), there was great difference between these two different regeneration patterns of forests SOC storage in 0-100cm layer was 7.13% higher in natural regenerated forest than that in artificial regeneration forest.(3) Different Regeneration patterns affected contents of LFOC and POC which decreased because of regeneration of the aged Chinese fir due to different regeneration, The decline of LFOC and POC was significant in artificial regeneration forest, Whereas the drop of them was slowly in natural regenerated forest, LFOC showed significant differences between the aged Chinese fir and artificial regeneration forest, while POC was not significant (P<0.05).(4) Different regeneration patterns affected soil microbial biomass carbon (MBC). Regeneration of the aged Chinese fir forest, MBC increased in natural regeneration, while decreased in artificial regeneration. MBC of the natural regenerated forest was 1.42 and 1.72 more than that of the aged forest's and artificial generation's, and the difference was remarkable between each of them.(5) Different regeneration patterns affected soil respiration differently. Compared with the aged Chinese fir, the soil respiration rate was increased by 32.41% in clear cutting natural regeneration while was decreased by 22.23% in controlled burning artificial regeneration. And the soil respiration rate of natural regeneration forest was obviously higher than that of artificial regeneration forest.(6) There are obviously differences in root respiration due to different regeneration patterns, root respiration rate was obviously higher in natural regenerated forest than that in the aged Chinese fir forest and artificial regeneration forest, the former's was 2.14 times and 2.02 times of the laters' respectively. And there was significant difference (P<0.05) between the aged Chinese fir forest and artificial regeneration forest.(7) Different regeneration patterns affected the respiration rate of litter. Respiration rate of litter in artificial regeneration forest was 29.7% higher than that in the aged Chinese fir forest, while the respiration rate of litter in natural regeneration forest was 33.8% lower than that in the aged Chinese fir forest, And the difference between them was obviously.( 8 ) Different regeneration patterns affected respirations rate of root-free soils. After the regenerations of the aged Chinese fir forest, respirations rate of root-free soils decreased both in artificial regeneration forest and natural regeneration forest, declined by 40.4% and 38.4% respectly, there was significant difference between regenerations forests and the aged Chinese fir forest. But no significant difference was shown between different kinds of regenerations forests.