Effect Of Succession On Soil Carbon Pool Of Evergreen Broad-Leaved Forests In Ningbo,Zhejiang

Since the Industrial Revolution, human activity is making the global warming more and more serious. In addition, land-use change has weakened carbon sequestration of the biosphere, which have a profound impact on the global ecosystem carbon cycle. Accumulation and decomposition process of forest soil carbon pool has a direct impact on the global carbon balance. It has become the focus of the current study that how to control the further development of the global warming, and sequester carbon from atmosphere to forest soil. There is a lack of the discovery on the mechanism about the stability of soil carbon pool, although many researchers have paid attention to successional dynamic of soil carbon.In this study, three successional stages(Early:Ⅰ, Middle:Ⅱ, Late:Ⅲ)with three repeat plots were choosed as object in Ningbo. In order to clarify the ecological mechanisms about successional dynamic of soil carbon pool, SOC and its active components (MC, MBC, DOC and ROC) were determined from 2013 to 2014. At the same time, we setted up collect-box in every plot, and collected the litterfall at the end of each month. Moreover, floor litter and fine roots were collected in each quarter. Then, we measured biomass and carbon content of vegetation carbon return. Finally, dynamic mechanism of soil carbon pool were analyzed by establishing SE, considering the chemical structure of soil organic carbon in litter, fine roots, humus and soil.The results showed that:(1) With the succession, SOC content increased significantly, namely:Ⅰ< Ⅱ< Ⅲ(P< 0.05). In addition, SOC stock of Ⅰ was lower than others(P< 0.05). But there was no significant difference between Ⅱ and Ⅲ(P> 0.05).(2) The content of soil Mineralizated carbon (MC), Microbial biomass carbon (MBC), Disolved organic carbon (DOC) and Readily oxidizable carbon (ROC) showed a significant upward trend with the succession(.P< 0.05). MC and MBC content of Ⅰ was significantly lower than Ⅱ and Ⅲ(P< 0.05), but the difference was not significant between the latters (P> 0.05). By the analysis of soil active carbon stock, we found that different components had different response for succession. MC, DOC and ROC stocks of Ⅰ were significantly lower than Ⅱ and Ⅲ(P< 0.05). However, the difference between MC stocks of Ⅱ and Ⅲ was not significant(P> 0.05); DOC stock of Ⅲ was significantly lower than Ⅱ(P< 0.05); in contrast, ROC stock of Ⅲ was significantly higher than Ⅱ (P< 0.05).The difference of MC/SOC and MBC/SOC among adjacent successional stages was not significant (P> 0.05). Meanwhile, DOC/SOC was significantly higher than Ⅲ(P< 0.05), but there was no significant difference among adjacent successional stages(P> 0.05). In addition, succession led to the significant increase of ROC/SOC ratio(P< 0.05).(3) Annual litterfa.ll biomass increased significantly from Ⅰ (7.48 t·hm-2) to Ⅲ (t·hm-2) with the succession(P< 0.05). For the carbon content of litterfall, Ⅲ was significantly higher than others(P< 0.05), but the difference between I and II was not significant(P> 0.05). Consistent with the change of annual litterfall biomass, succession increased litterfall carbon stock significant(P< 0.05), and III reached the highest value (5.686 t· hm-2).Forest floor biomass decreased significantly with the succession(P< 0.05), from Ⅰ (20.75 t·hm-2) to Ⅲ(13.18t·hm-2). And carbon content of Ⅱ was significantly higher than I (P< 0.05), but there was no significant difference among adjacent successional stages(P> 0.05). Similarly with carbon content, the difference of floor litter carbon stock among adjacent successional stages were not significantly(P> 0.05), but Ⅰ was significantly higher than Ⅲ(P< 0.05).In the process of secondary succession, fine roots biomass increased significantly from Ⅰ (0.79 t·hm-2) to Ⅲ(2.83 t·hm-2) (P< 0.05). But the carbon content of fine roots decreased significantly(P< 0.05). In addition, the carbon stock of Ⅰ was significantly lower than Ⅱ and Ⅲ, but the difference between Ⅱ and Ⅲ was not significant(P>0.05).(4) Alkyl carbon/alkoxyl carbon (A/O-A) and hydrophobic carbon/hydrophilic carbon of soil increased with the succession, while its aromaticity tended to decrease. For litterfall and fine roots, their proportions of alkyl carbon and carbonyl carbon were significantly lower than that of humus and soil(.P< 0.05), and the proportions of alkoxyl carbon and aromatic carbon were significantly higher(P< 0.05). Then A/O-A and hydrophobic carbon/hydrophilic carbon of litterfall and fine roots were also lower than that of humus and soil(P< 0.05).(5) According to Pearson analysis, significant positive correlation was found between SOC carbon stock and active carbons(MC,MBC,DOC,ROC) (P< 0.05), as well as litterfall and fine roots(P< 0.05). However, SOC carbon stock was negative correlated with floor litter(P< 0.05). Meanwhile, there was significant correlation among active carbon components(MC, MBC, DOC, ROC) each other(P< 0.05). Besides, soil carbon was not significantly correlated with carbon’s chemical structure of litter fall, fineroots, humus and soil respectively(P> 0.05).(6)The results of path analysis shown that succession directly affected soil carbon pool, which was much lower than its indirect effect by other factors. In addition, in the process of succession, all factors can jointly explained 65% of SOC change.To sum up, in the evergreen broad-leaved forest succession increased the vegetation carbon return and soil active carbon, which furtherly led to the accumulation of soil organic carbon pool.