| Forest carbon sequestration is significant for terrestrial carbon cycle and global carbon balance.The present study aimed to estimate the 37-year-old Cunninghamia lanceolata?Lamb.?Hook.plantation in Daqingshan,Guangxi,South China.The organic carbon content data of different tree organs?stem,branch,leaf,root head and root?,shrub,herb,litter and soil in Chinese fir stand were obtained by using stem analysis,sample method and profile analysis.The following contents were studied mainly:?1?Construction of biomass compatibility model;?2?Effect of diameter,density and site on biomass allocation of individual tree;?3?Effect of density,site and soil depth on soil organic carbon density;?4?Carbon storage allocation of different initial planting densities and site indices of mature Chinese fir forest ecosystem,We found that:1.The biomass compatibility model of Chinese fir organs and individual tree established with DH as independent variable had the best fitting effect.The prediction accuracy of stem and individual biomass was more than 95%,and the prediction accuracy of leaf,branch,root head and root biomass was over 80%.2.Branches,leaves,stems,root heads,roots and total biomass of Chinese fir increased significantly with the increase of diameter.The ratio of biomass of different organs to biomass of individual tree was:stem>root head>branch>root>leaf,of which the ratio of stem biomass to individual tree biomass was the largest,accounting for 71.35%?80.47%,and the ratio of leaves biomass to individual tree biomass was the smallest.The biomass of individual tree and organs of Chinese fir decreased with the increase of initial planting density,and increased with the increase of site index.The initial planting density had a smaller impact on the biomass allocation than site index,which showed that the ratio of biomass of the leaves,stems and root heads to individual tree decreased with the decrease of the site index,while the ratio of biomass of branches and roots biomass to individual tree decreased.3.The average soil organic carbon content and carbon density of 0?100 cm in Chinese fir plantation were 8.81?11.80 g·kg-1and 133.82?181.22 Mg·hm-2,respectively.At the same initial planting density,soil organic carbon content and carbon density increased following the rule of14>10>16>18 m.At the same site index,the soil organic carbon content and carbon density increased following the rule of 1667>3333>5000>10000>6667 plants·hm-2,indicating that soil organic carbon content and carbon density in the stand with medium and low initial planting density were higher than those in the stand with high initial planting density.Soil organic carbon content and carbon density decreased with increasing soil depth,but the decline range was different,the decrease range of 0?30 cm was larger,and there were significant differences in soil organic carbon content and density among different soil layers?P<0.05?.The decrease range of 50?100 cm was smaller,and there was no significant difference among different soil layers.The 0?30 cm soil layer stored 44.61%?49.97%of the total,which had an important contribution to the soil carbon storage.The organic carbon density of each soil layer was negatively correlated with the stand index.4.The content of organic carbon in different organs of tree was significantly different?P<0.05?,and followed the rule of stem(554.25 g·kg-1)>leaf(549.74 g·kg-1)>branch(540.49g·kg-1)>root head(533.26 g·kg-1)>root(531.11 g·kg-1),the average organic carbon content of the understory vegetation showed litter layer(506.7 g·kg-1)>shrub layer(476.7 g·kg-1)>herb layer(448.2 g·kg-1).The carbon storage and the proportion of tree organs were as follows:stem>root head>branch>root>leaf,the average carbon storage stored in aboveground was 86.40%,and in root head and root was only 13.60%.The carbon storage of different organs varied with the initial planting density and site index.In general,the carbon storage of leaf,stem and root head increased with the increase of initial planting density,and decreased with the increase of site index,while branch and root showed opposite change rule.The carbon storage of Chinese fir plantation ecosystem was 238.60 Mg·hm-2,and the average carbon storage allocation of each component was ranked as:soil layer(156.67Mg·hm-2)>tree layer(Mg·hm-2)>litter layer(2.41 Mg·hm-2)>herb layer(1.62 Mg·hm-2)>shrub layer(0.99 Mg·hm-2),which accounted for 65.66%,32.24%,0.42%,0.68%and 1.01%,respectively.The site index affected the response of tree layer and ecosystem carbon storage to initial planting density.When the site index was 10 m and 14 m,the carbon storage of tree layer and ecosystem increases with the initial planting density.While the site index is 16 m and18 m,the carbon storage of tree layer and ecosystem decreases with increase of initial planting density.At the same initial planting density,the tree layer carbon storage and the proportion increased with the increase of site index,while the carbon storage of soil layer decreased with the increase of site index.The stand with the planting density of 6667 plants·hm-2 and the site index class of 14 m had the highest carbon storage with 278.86 Mg·hm-2,while the stand with the site index class of 10 m and planting density of 5000 plants·hm-2 had the lowest carbon storage(199.17Mg·hm-2). |
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