Characteristics Of Carbon Stocks And Stability Of Soil Organic Carbon Under Three Artificial Forest Types In Mid-Subtropics

The carbon pools of forest vegetation are an important component of carbon storage in terrestrial ecosystems. Soil carbon pools of forest ecosystems is the major component of forest ecosystems and is2to3times the carbon pools of forest vegetation. The carbon storage of artificial ecosystem have an important role in slowing down global warming. The soil samples under four forest types such as Chinese Fir, Slash Pine, Bamboo plantation and secondary forest in mid-subtropics were studied. The purpose of this research was to assess impact of forest types on the distributions of soil organic carbon(SOC)、active soil carbon fractions(MBC、WSOC、ROC)、slow carbon fractions(LFOC and POC) and water-stable aggregates, and understanding how these SOC fractions behave in response to changes in land use will aid in discussing the mechanism of stability of SOC under different forest vegetation types.At last, the carbon storage of artificial ecosystem in Zhejiang provinces was evaluated. Major conclusions were summarized as follows:(1) The content of profile SOC decreased as the soil depths increased under four forest soils. The SOC was significant difference in0-30cm layers among the four forest soils (p<0.05), which were in the following order:secondary forest> Chinese Fir> Bamboo plantation> Slash Pine, but no difference in30-100cm layers. Soc in soil increased with increasing ages of Chinese Fir, while decreased with increasing ages of Slash Pine. Significant difference (p<0.05) was detected between10years and30years in Chinese Fir and Slash Pine.The vertical distribution of SOC densities showed the same trend as the SOC content in soils of different forest types and ages except Bamboo plantation. And the SOC densities were mainly stored in the0-30cm soil layers, which accounted50%of the total SOC densities except20a old Slash Pine and Moso bamboo. The SOC densities in0～100cm layers from the highest to the lowest were ranked as follows:Slash Pine10a> Chinese Fir30a>Secondary forest> Slash Pine20a> Moso bamboo> Chinese Fir20a> Chinese Fir10a> Slash Pine30a.(2) The effects on soil aggregates were focused on the size groups of>5mm and2-5mm under different forest types. As the percentage of water-stable aggregates of the size groups of>5mm and2-5mm were significant differences among different forest in all layers (p<0.05). The total content of SOC showed a positively linear relationship with the content of aggregates SOC of the size groups of0.25-2mm, while>2mm groups didn’t. The SOC of>2mm groups were instable carbon, liable to participate in soil carbon cycle.The results of R0.25and the content of MWD all were in the following order: Secondary forest>Chinese Fir>Slash Pine、Bamboo plantation, which showed that the stability of forest soil aggregate of Secondary forest was the highest, Chinese Fir took the second place, Slash Pine and Bamboo plantation were the lowest.Results show that the content of SOC in aggregates of the same layer in different foresnt types and times increased as the soil depths decreased. The different of content of SOC in aggregates had significant differences only in0～10cm layer, showing a sequence of Secondary forest>Chinese Fir30a>Slash Pine30a>Bamboo plantation. And the sequence for different ages of Chinese Fir and Slash Pine were Chinese Fir30a>Chinese Fir10a>Chinese Fir20a, Slash Pine20a>Slash Pine10a> Slash Pine30a, respectively.The active SOC content such as MBC and ROC showed the same trend as the SOC content in soils of different forest types and ages, and content from the highest to the lowest were ranked as follows:Secondary forest>Chinese Fir>Bamboo plantation>Slash Pine, but there was no difference among the three forest soils. ASOC/SOC ratio represents the stability of SOC; from the results we can see that the stability of SOC in top soil from the highest to the lowest was ranked as follows:Chinese Fir> Secondary forest> Slash Pine> Bamboo plantation.The result of slow Carbon showed that:The LFOC was no significant difference in0-30cm layers among the four forest soils, which were in the following order:Bamboo plantation> Chinese Fir> Slash Pine> secondary forest. In0-30cm layers, the LFOC/SOC ratio of secondary forest was higher than other three forest types, especially was significantly higher than Bamboo plantation and Slash Pine (p<0.01). The content of POC in the same soil layers under different forest were in the following order:Secondary forest> Chinese Fir> Slash Pine> Bamboo plantation. There were significant differences among different forest in0-10cm soil layer (p<0.01), while no difference in10-30cm layer. In0～30cm layer, the POC/SOC ratio of secondary forest was significantly higher than other three forest (p<0.01), Chinese Fir took the second place. Bamboo plantation and Slash Pine were the lowest. The results of relationships among LFOC、POC and soil nutrients showed that POC is more suitable for representing the slow carbon pool in forest soil.(3) The analysis on soil organic carbon and other chemical quality indicators showed that, the soil organic carbon have a significant correlation on nitrogen, phosphorus, as well as quick nitrogen, phosphorus and potassium in Chinese Fir plantation and slash Pine forest. The correlation of organic carbon with total nitrogen and total phosphorus is significant in bamboo ecosystem, but because of the strong Human activity strength, fertilization, tillage and other management measures, the state of soil available nutrient composition of soil organic carbon are changed.So the correlation Phyllostachys pubescens with quick-nitrogen, phosphorus and potassium is not significant. Compared with Chinese Fir plantation, slash pine forest and bamboo eco-systems, the secondary forest have a smaller interference by external. It is a natural recovery process of succession. Soil nutrients mainly come from circulation of the self-loop secondary forest ecosystems. The correlation coefficient of the soil organic carbon with total nitrogen, nitrogen-speed, speed phosphorus and potassium-speed is highest in all forest types, as well as the relevance.(4) The study of plant carbon density of different species and recovery time has show that the carbon density of chinese fir and slash pine plantation tree layer was significantly greater than bamboo forest and secondary forests. In various organs, slash pine plantation tree trunks, branches and roots were significantly higher than bamboo forest and secondary forests, chinese fir forest trunks were significantly higher than bamboo forest and secondary forests. In various organs of secondary forests, in addition to the carbon density of underground root was significantly greater than the underground sections of bamboo, the rest were not significantly different, also found that the carbon density of slash pine plantation and secondary forests tree tree layer layer underground is relatively large, were more than25%, while the chinese fir forest and bamboo forest is relatively low, both at15%or less.For the organic carbon in terms of the different sub-libraries, the organic carbon density of litter layer is the lowest. The organic carbon density of plant soil organic and1m soil layer is40.78～120.43t·hm-2and53.0～138.4t·hm-2. Its reserves are much higher than the litter layer. Soil carbon pool has a greater potential of carbon sequestration, the organic carbon density of lm soil layer is higher than the sum of Plant floor and plant litter layer. In terms of different stands, the carbon density of over-ground floor from high to low is pine30a>pine20a>fir30a>fir20a>secondary forest>pine10a>Bbamboo> fir10a. The organic carbon density of1m soil layer show that pine10a>fir30a>secondary forest> pine20a> Bbamboo>fir20a>fir10a>pine30a. Stand total carbon density (aboveground+1m soil layer) were as follows:fir30a>pine20a>secondary forest>pine10a>fir20a>pine30a> Bbamboo>fir10a.The carbon intensity of fir the soil and plant litter layer is a positive correlation, and the the carbon intensity of1m soil carbon density and plant litter layer is a significant correlation, while slash pine plantation is in the opposite trend. The correlation between organic carbon density of lm soil and plant litter layer carbon layer is a negative in bamboo forest, but have not reached the significant level.(5) According to forest resources inventory data of Zhejiang Province, we estimated the total carbon storage of the secondary forest, as well as fir plantation and bamboo forest which are two kinds of plantation eco-system.The results showed that ordering of the total carbon storage in different types of ecosystem is:secondary forest>fir plantation> bamboo forest., and the ordering of carbon storage in different fir forest age is:mature forest>middle-aged forest>young forest. The total carbon storage of the three kinds of ecosystems is1.0457Pg C. The ordering of the carbon storage in different soil layer is:soil layer>tree layer> litter layer>shrub and herb layers. The respective percentage is60.7%,35.5%,3.43%and0.36%to total. Further discussion and analysis also showed that soil carbon sequestration plantations have great potential in Zhejiang Province. If plantation in Zhejiang Province dominated by the young and middle-aged forest, as the growth of the carbon storage in the young forest and middle-aged forest, carbon storage will be further expanded, plantation carbon sinks feature will be enhanced markedly.At the same time, reforestation and other activities can increase the plantation areas and contribute significantly to the improvement of soil carbon storage. In addition, strengthening the operation and management on plantations can also further enhance the level of productivity, enhance carbon storage capacity of the systems.