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Co-accumulation Characters Of Carbon And Nitrogen In Soils Under Two Forest Types In Changbai Mountain

Posted on:2019-05-02Degree:MasterType:Thesis
Country:ChinaCandidate:Y SunFull Text:PDF
GTID:2370330548474139Subject:Soil science
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The stability of forest soil carbon pools is crucial to the global carbon cycle.Changbai Mountain forest ecosystem is one of the most important forest ecological resources in the north of China,and its soil organic carbon reserves are huge.However,the study on its organic carbon stability is relatively lacking.The study focused on the soils of two typical forest types(Virgin Korean pine forest and Polar-birch secondary forest)in the Changbai Mountain forest area.The dry sieve method was used to analyze the distribution of organic carbon and nitrogen in each size class of aggregates.The density grouping method was used to further study the density components of organic carbon and nitrogen and their distribution in aggregates.The mechanism of the stabilization of organic carbon and nitrogen in soil was explored.The main findings are as follows:(1)The content of soil organic carbon and total nitrogen in the polar-birch secondary forest was significantly higher than that of the virgin Korean pine forest,and the average between layers(0-50 cm)was 1.5 and 1.3 times that of the latter.This shows that forest types have a significant effect on soil organic carbon and nitrogen content.China's forest planning and management of forest ecosystems should focus on the impact of forest types on the accumulation of soil organic carbon and nitrogen pools.(2)The total organic carbon and nitrogen content in soil decreased significantly with the increase of soil depth.The content of soil organic carbon and nitrogen in the 0-5 cm layer of the two forest types was the highest.The soil organic carbon content was 123.55 g/kg,accounting for 64.2%of the entire profile;the soil total nitrogen content was 11.00 g/kg,accounting for 53.8%of the entire profile.This indicates that the surface soil contributes significantly to soil organic carbon and nitrogen pools.Therefore,strengthening the protection of surface soil to maintain and increase soil carbon and nitrogen reserves is of great significance for improving global warming and reducing the concentration of greenhouse gases in the atmosphere.(3)The proportion of average(0-50 cm)>0.25 mm aggregates(PA0.25)content between two forest types.The virgin Korean pine forest was 91.58%higher than that of the polar-birch secondary forest 84.76%.This indicates that the virgin Korean pine forest has better soil aggregates performance and a more stable structure than that of polar-birch secondary forest.In addition,the content of>2 mm aggregates changes significantly with the deepening of the soil layer.The forest types from 0-5 cm to 5-15 cm,5-15 to 15-30 cm,and 15-30 cm to 30-50 cm decreased by 33.0%,37.0%,and 25.9%,respectively.The content of aggregates of 2-1 mm,1-0.25 mm,and<0.25 mm was relatively stable.This indicates that large-diameter aggregates have a large variability in the soil,a faster turnover rate,and are more likely to be broken or lost due to factors such as the external environment and human interference,resulting in a decrease in their content,resulting in soil organic carbon,Nitrogen storage stability is reduced.Therefore,the study on the stability mechanism of macro-aggregates is of great significance for the sequestration of organic carbon and nitrogen in the soil.(4)The correlation analysis of total organic carbon and aggregate organic carbon and nitrogen in soil showed that the total organic carbon in the soil was closely related to the organic carbon and nitrogen of 1-0.25 mm and<0.25 mm aggregates,with the coefficient of determination(R2)being 0.976,0.928,and 0.966,respectively.0.949.This indicates that the total soil organic carbon and nitrogen accumulation in the studied area was mainly affected by the organic carbon and nitrogen contents of 1-0.25 mm and<0.25 mm aggregates.In addition,the more organic carbon and nitrogen are stored in the small-diameter aggregates in the soil,the stronger the stability of organic carbon and nitrogen in the soil,and the greater the ability of the soil to fix carbon and nitrogen,which is consistent with the soil organic carbon and nitrogen.This is consistent with the hierarchical theory that the input of soil organic carbon and nitrogen is preferentially accumulated in small-diameter aggregates.(5)The soil organic carbon content in the 0-5 cm and 5-15 cm layers of the polar-birch secondary forest was significantly higher than that of the virgin Korean pine forest,but the proportion of heavy organic carbon(HF-C)was significantly lower than that of the latter.This shows that even if secondary success promotes the retention of organic carbon in the soil,it also reduces the overall stability of the soil organic carbon pool.Therefore,strengthening the protection of primary forest resources and promoting secondary forest ecological restoration in Changbai Mountain area is of great significance for increasing the stability of soil carbon pools.(6)The distribution ratio of free light fraction organic carbon(FLF-C)gradually decreases with the increase of aggregate size,while HF-C shows an increasing trend.This shows that large aggregates(>0.25 mm)are rich in more active organic carbon.With decreasing diameter,the proportion of active organic carbon is gradually reduced,while inert organic carbon is gradually increased,which strengthens the stability of organic carbon in small-diameter aggregates.(7)The occluded light fraction organic carbon(OLF-C)is less than 5%of total organic carbon,and its distribution ratio gradually decreases as the aggregate size decreases.This part of the organic carbon is relatively stable under the protection of aggregates,increasing the stock of soil stability carbon stocks.(8)There was significant or extremely significant positive correlation between soil total organic carbon and total nitrogen,and there were significant co-accumulation characteristics in different soil layers and under different forest types.In the soil density components,the free light fraction(FLF),the occluded light fraction(OLF)and the heavy fraction(HF)and even the FLF,OLF and HF in the soil aggregates,organic carbon and nitrogen also showed significant or extremely significant positive correlations.It shows that there is a coupling of carbon and nitrogen accumulation in each component.
Keywords/Search Tags:Forest soil, Organic carbon, Carbon-nitrogen coupling, Density component, Aggregates
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