Study On The Carbon Storage And Soil Respiration Of Three Forest Ecosystems In The Mid-subtropical Zone, China

Abstract: The carbon cycle of forest ecosystems plays an important role in the global carbon cycle, which is closely related to CO₂ concentration in atmosphere and has an obvious effect on composition of atmospheric elements. To improve the estimation accuracy of forest ecosystem carbon cycle would help forecast the change of climate in the future. At present, the man-made forest area in China come to be more than 53 million hectares, being number one in the world, but there are few data on the carbon cycle of forest plantation ecosystem in the China South, which is the major zone of forest plantation in China, limiting the exact estimation on the carbon sink or source of the man-made forest ecosystem in the South of China, and the function of the adjustment on the climate. So three major forest plantation in Fujian has been study on the carbon storage , soil respiration and carbon balance to provide the reference on the carbon cycle on the forest plantation ecosystem in China south. The results were showed as follows:1. There were differences among carbon content of different growing stage in tree organs (leaf, branch, stem, bark and root), understory layer, litter layer and soil layer, so was that of different forest including the Chinese fir forest plantation (CLP), Pinus massoniana Lamb forest plantation (PMP) and Pboebe bourmei forest plantation (PBP). There were differences among the carbon content of the tree different organs, moreover the sequence of organs varied in different age and stand types. The soil carbon content increased with the increase of age at the same soil layer; the soil carbon content sequence of different forest types was PBP> CLP> PMP, moreover the difference decreased with soil depth increase, and there was no difference at 100cm depth. The soil organic carbon concentration generally decreased with the increase of depth in all stand types, and the maximum differences of soil carbon content for adjacent soil layer occurred at the 0²0cm and 20⁴0cm soil layer.2. The carbon storage of three forest plantation ecosystems increased with the increase of age. and the sequence of carbon storage of three forest plantation for the same growing stages was PBP>CLP>PMP but the carbon storage of understory layer did not show the consistent orderliness. Soil carbon storage was the main carbon pool of the forest ecosystem, showing agenerally increasing trend with increasing age, but the proportion of total carbon storage showing a generally decreasing trend with increasing age, but the reverse was the tree, which was the main body of the difference among carbon storage of different growing stages, but the difference among three forest types were caused by the cooperation of soil and tree. The litter carbon storage possessed little proportion of ecosystem carbon storage, but being link pooling connecting generation and soil, the litter produced important impact on the forest ecosystem.3. Based on the data of annual net production and relevant carbon content, the annual carbon net fixation of PBP,CLP and PMP was 3.719 ⁷.648t ? hm"2 ? a"1, 3.44 — 7.149t ? hm"2 ? a"' $\ 2.863 ⁵.683 t ? hm"2 ? a"',respectively, showing a generally trend MAP(middle-aged plantation)>YP(young plantation)>MP(mature plantation), caused by the difference of the annual carbon net fixation of tree. For the same growing stage, there was difference among the annual carbon net fixation of three forest types, caused by the difference of the annual carbon net fixation of tree and litter.4. With enclosed chamber method, this paper studied the dynamic of the soil respiration in PBP. CLP plantation and PMP. The results showed that there was significant differences in soil respiration amog the various forest types and the highest was in PBP then in CLP, and the lowest was inPMP. The difference has been caused by the difference among root mass, litter mass and soil carbon content of various forest, which in PBP was as much 1.77 times ,2.82 times, 1.03 times as that in CLP, and 2.20 times , 2.87 times, 1.05 times as that in PMP.But the seasonal and daily pattern of soil respiration in three forest types could be expressed as a one-humped curve, and the highest values appeared at July and 14:00, which was similar to the change of air temperature.5. The relationship between soil respiration and temperature and soil water content was analyzed using the regression analysis of the SPSS and the result showed: there was a good exponent correlation between soil respiration and temperature, especially the soil temperature at 5 cm depth. The Qio value of Chinese fir plantation was higher than that of the other two, which implied that the sensitivity of soil respiration to temperature in Chinese fir plantation was highest. There was a good linear correlation between soil respiration and the soil water content in the upper 20 cm of soil. The relationship between soil respiration rate and the two...