| Forest, the main body of carbon sink in terrestrial ecosystem, plays a critical role in carbon balance and cycle. A lot of study, however, mainly focused on the carbon store of tree layer in the forest carbon budget with the lack of investigation on understory, litter, and soil carbon, which is essential for accurate and quantitative evaluation of forest carbon sequestration and mechanisms. In this study, two typical forest ecosystems, a Chinese pine(Pinus tabulaeformis) plantation and a natural secondary oak forest were investigated in Shaanxi Province. The carbon pool constitution and difference between regions(north, central, and south) and forest age groups(young, middle-aged, and mature) in the two typical forest ecosystems were studied. Relationship between carbon pools were explored and discussed further. Finally, the impacts of biotic and abiotic factors on carbon pool constitution were analyzed based on principal component analysis and redundancy analysis. The main results can be concluded as follow:(1) The proportion occupied by tree, bush, herb, litter and soil carbon pool component was 34.54%, 0.81%, 0.54%, 2.91%, and 61.21% in Chinese pine plantation ecosystem, and 34.73%, 1.24%, 0.36%, 2.18%, and 61.49% in oak forest ecosystem, respectively. The soil carbon store was twofold than that of tree pool, and both contributed greatly to forest ecosystem carbon stock, accounting for 95.75% and 96.22% in two typical forest.(2) Carbon storage in tree layer was positively correlated with carbon store in bush, litter, and soil layer, and negatively correlated with carbon store in herb layer in Chinese pine plantation. No obvious associations occurred between tree layer and other layers in oak forest, although negatively insignificant relation existed between carbon store in tree layer and bush, herb layer. After combining herb with bush layer into understory layer, tree, bush and herb into vegetation layer, and tree, bush, herb and litter into aboveground layer, we found that there existed an positively relation between carbon store in vegetation layer and in litter layer, between aboveground layer and belowground layer in Chinese pine plantation. And tree carbon stock was negatively related to understory stock in oak forest.(3) Principal component analysis showed that carbon stock composition in Chinese pine plantation mainly changed with forest age groups. And carbon store in tree, bush, litter, and soil layer increased while herb carbon stock decreased with the increase of forest age. However, carbon stock composition predominantly varied along regions in oak forest. The tree and soil carbon stock increased while bush, herb, and litter stock declined from north to central and south in Shaanxi. Besides, topography, meteorology, and nutrient could together explain 66.86% and 40.94% of the total variation of carbon stock composition in Chinese pine and oak forest, respectively. Moreover, forest cover and AMT had a significant effect on carbon stock composition in Chinese pine plantation(p<0.01), while height, AMT, and MAP exerted significant impact in oak forest(p<0.05).(4) The investigation on carbon inventory of forest ecosystem should be based on forest inventory and field sampling data with different estimation methods to minimize the uncertainty. The Application of correlation between carbon pools should be also cautious. Moreover, the difference of carbon stock composition between species in response to climate factors ought to be taken further into consideration with depth analysis of the hidden biological mechanism and exploring techniques to increase carbon store. |
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