| The vertical distribution of soil organic carbon (SOC), total nitrogen (TN) and labile organic carbon (LOC) content and storage of SOC, TN in the depth of 0-75 cm were contrasted and discussed by sampling and laboratory analysis under primary Cunninghamia lanceolata (Chinese fir) forests converted with regeneration patterns of a) secondary Chinese fir forests, b) natural woods, c) Castanea mollissima plantations, d) Citrus reticulata plantations and e) Andropogon chinensis grass in Huitong County of Hunan Province. With Chinese fir 20 years forestlands as a contrast, the thesis compares soil carbon pool management index of lands with five regeneration patterns, explores the difference of soil carbon sequestration capacity of land under different regeneration patterns and provides basis data and scientific evidence for forests carbon pool estimation and soil sustainable utilization under artificial activities. The results show that:1. SOC content and density distribution characteristics of forestlands with five regeneration patterns:(1) SOC content had the exponential function decreasing trend with the increase of soil depth under different regeneration patterns (r2≥0.929). The sequence of mean SOC content of 0-75 cm was C. mollissima (14.76g·kg-1)> Chinese fir 12 years (13.54g·kg-1)> Chinese fir 20 years (12.81g·kg-1)> natural woods (11.50g·kg-1)> C. reticulata (10.73g·kg-1)>A. chinensis grass (10.09g·kg-1). Mean SOC content of C. mollissima was significantly higher than that of C. reticulata and A. chinensis grass (p<0.05), and mean SOC content of Chinese fir 12 years was significantly higher than A. chinensis grass (p<0.05), but it was not significant among Chinese fir 20 years, natural woods and A. chinensis grass (p>0.05,). Among adjacent soil layers, SOC contents of Chinese fir 12 and 20 years are significantly higher than adjacent soil layers of 0-15 cm(p<0.05), difference is insignificant between adjacent soil layers in other forestlands(p>0.05).(2) Forestlands under five regeneration manners, of which SOC density of 0-15, 0-30,0-45,0-60 and 0-75 cm soil layers ranking from high to low showed:C. mollissima>Chinese fir 12 years>Chinese fir 20 years>A.chinensis grass>natural woods>C. reticulata. Compared with SOC density at the time of primary Chinese fir 22 years forests cutting, in the depth of 0-60 cm soil layer, SOC density decreased after primary Chinese fir converted into secondary Chinese fir 12 and 20 years, natural woods, C. mollissima, C. reticulata and A. chinensis grass and annual reduction rate was 1.769%,1.666%,2.000%,1.373%,2.223% and 2.044% respectively.2. LOC content distribution of forestlands with five regeneration patterns:(1) LOC content had the line decreasing trend with the increase of soil depth under different regeneration patterns (R2≥0.731). In the 0-75 cm soil depth, mean LOC content was 1.100-1.800g·kg-1, and the sequence of it was natural woods (1.713g·kg-1) >Chinese fir 20 years (1.625g·kg-1)> Chinese fir 12 years (1.406g·kg-1)> A. chinensis grass(1.314g·kg-1)> C. reticulata(1.260g·kg-1)>C. mollissima (1.119g·kg-1).(2) In the 0-75 cm soil depth, the frication of soil LOC content had different changing ways with the increase of soil depth under different regeneration patterns. Mean frication of soil LOC content was 0.07-0.15 under different regeneration patterns. And mean frication of soil LOC content of Chinese fir, natural wood and C. reticulata, A. chinensis grassland had significantly higher than that of C. mollissima (p<0.05), and mean frication of soil LOC content of Chinese fir 20 years and natural woods had significantly higher than that of Chinese fir 12 years (p<0.05), but it was not significant between the others forestlands (p>0.05)3. Soil TN:distribution and storage with five regeneration patterns.(1) TN content had the line function decreasing trend with the increase of soil depth under different regeneration patterns (R2≥0.701). In the 0-75 cm soil depth, the sequence of mean TN content was C. mollissima (1.68g·kg-1)> Chinese fir 12 years (1.57g·kg-1)> Chinese fir 20 years (1.47g·kg-1)> A. chinensis grass (1.04g·kg-1)> natural woods (1.38g·kg-1)> C. reticulata (1.31g·kg-1).(2) Forestlands under five regeneration manners, of which TN density of 0-15,0-30,0-45,0-60,0-75 cm soil layers ranking from high to low showed:C. mollissima> Chinese fir 12 years>A. chinensis grass>natural woods>C. reticulata>Chinese fir 20 years.4. Effect of slope aspects on content of SOC, TN and LOC of Chinese fir was changing with the cultivated years. With the growth of Chinese fir, Chinese fir forest on the left (East) slope had a greater contribution on SOC density in deep soil than that on the right (West) slope. The soil TN of Chinese fir forest on the left (East) slope had a greater accumulating rate than the right (West) slope. TN density of the left (East) slope soil had exceeded that of the right (West) slope with the growth of Chinese fir.5. With Chinese fir 20 years forestlands as a contrast, soil carbon pool management index with five regeneration patterns had a uneven. Soil carbon pool lability (L), carbon pool lability index (LI) and carbon pool management index (CMI) of natural woods were higher than 14.12%,21.60% and 18.33% those of the contrast lands respectively, while those of Chinese fir 12 year, C. mollissima and C. reticulata were lower, of which L decreased by 21.67%,2.10% and 87.18% respectively, of which LI decreased by 47.34%,48.99%, and 27.07% respectively. L and LI of A. chinensis grass increased by 7.01%,23.50% respectively, while CMI of that was higher than that of contrast lands but lower than that of C. reticulata plantation lands. Soil carbon pool index of Chinese fir 12 year and C. mollissima increased by 15.60% and 23.30%, while that of natural woods, C. reticulata and A. chinensis grass lands deceased 0.50%, 11.50%,17.40% respectively.6. There were the negative correlations between SOC, TN, LOC, CMI and bulk density but there were no obvious law between SOC, TN, LOC, CMI and soil moisture content, pH.
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