Changes Of Forest Soil Oranic Carbon And Nitrogen Pools As Driven By Secondary Succession In Changbai Mountain

In the context of global climate change,forest soils play an increasingly important role in the carbon balance and carbon sequestration of terrestrial ecosystems.Changbai Mountain Nature Reserve is one of the three major forest areas in Northeast China,and it has a relatively complete temperate mountain forest ecosystem.Broad-leaved Korean pine forest is the most important top community in the northeastern forest region of China.In recent years,due to the disturbance of human activities,broad-leaved Korean pine forest has been gradually replaced by Yanghua secondary forest.Secondary succession is an important driving factor for the change of organic carbon and nitrogen pool in forest soil.In this paper,the BPy(Betula Platyphylla Secondary Forest(young stand)?BPm(Betula Platyphylla Secondary Forest(half-mature))?HWo(Hard Wood Mixed Forest(old growth))and KPy(Broad-leaved Korean Pine Forest(virgin))in Changbai Mountain were used as examples to systematically study the quantitative distribution of soil organic carbon and nitrogen in forest soils.The synergistic accumulation characteristics of the temperate forest soil carbon pool and carbon sink effect and its carbon-nitrogen coupling mechanism were discussed.The main findings are as follows:The soil organic carbon and nitrogen contents in the four forest types were the highest in the surface layer,and decreased significantly with the depth of the soil layer.Except for the BPy,the average organic carbon content of 0-5 cm soil layer under the other three forest types is above 100g·kg-1,and the average organic carbon value of 5?10 cm soil layer is also as high as 50g·kg-1;The average nitrogen content of the 0?5 cm soil layer is as high as 5.4?8.3g·kg-1,and the average nitrogen value of the 5?10 cm soil layer is also as high as 3.1?5.9g·kg-1,indicating that the surface layer is 0?10 cm.And the main aggregate layer of total nitrogen,the carbon and nitrogen surface aggregation characteristics are obvious.The soil C/N is also the highest in the surface layer and decreases significantly with the depth of the soil layer.It indicated that the accumulation rate of soil organic carbon in surface soil was higher than that in total nitrogen,and it decreased significantly with the increase of soil depth.(2)Compared in different forest types,in 0?20 cm soil layer,the trend of organic carbon and nitrogen content are HWo>BPm>KPv>BPy.There was no significant difference in soil organic carbon and total nitrogen content between the four forest types in the 20?60 cm soil layer.In the 0?5 cm soil layer,the trend of C/N ratio is KPv>BPm>HWo>BPy,and the C/N of the 5?10 cm soil layer is basically the same as the upper soil layer,but the young forest The difference with the old forest is not obvious.The difference of four forest types in the soil layer below 10 cm is not obvious.This indicates that the effects of secondary succession or forest type on soil organic carbon and total C/N are only in the soil surface or subsurface,and the succession process is conducive to the increase of organic carbon and nitrogen.(3)The effect of organic carbon content in the upper soil layers of the middle and upper layers of the forests of the BPm and HWo is higher than that of the other two forest types,and this effect is only manifested in the soil surface or subsurface,and the deep soil is only Shows a certain relevant trend,but does not reach a statistically significant level.This difference in the four forest types may be partly related to soil animal activities,forest root distribution and other factors.The mixed or uniform decay of soil organic matter may be more pronounced in broad-leaved forests.(4)The organic carbon and total nitrogen in different soil types of the four forest types showed significant or extremely significant positive correlation.Compared with different soil layers,the determination coefficient of total nitrogen to total organic carbon in 0?5cm and 5?10cm soil layers(especially the former)is significantly smaller than that of the lower 10?20cm and 20?40cm soil layers,indicating that relative to the upper soil layer,The accumulation of organic carbon in the lower soil layer depends to a greater extent on the accumulation of total nitrogen.(5)Compared with different forest types,except for 0?5cm soil layer of KPv,the organic carbon and nitrogen in other soil layers showed significant or extremely significant positive correlation.There is no significant difference in carbon and nitrogen relationship between the four forest types(10?20cm,20?40cm,40?60cm),indicating that the influence of forest type or secondary succession on soil carbon and nitrogen is mainly reflected in the surface layer..(6)The total organic carbon and C/N of the four forest types also showed a positive correlation in the surface layer(0?5cm,5?10cm),indicating that the soil with high surface organic carbon content(sample plot),Its organic matter also has a higher C/N value(relatively lean nitrogen).For the normal lower soil layer(non-buried),the C/N value of organic matter is relatively stable,and the difference in organic matter accumulation between the plots may be mainly due to the strength of the soil formation process(leaching deposition,etc.)or other randomness,and factor determined.(7)Compared with organic carbon,the distribution of nitrogen is more inclined to recombinant components,and the accumulation of recombinant organic carbon(organic matter)depends to a greater extent on the accumulation of nitrogen-containing organic matter.There was no significant difference in the organic carbon and nitrogen storage between the forest type.However,the content of organic carbon and nitrogen,the reserves and distribution ratio of the secondary forests of Betula Platyphylla Secondary Forest were significantly higher than those of the Broad-leaved Korean Pine Forest,and the C/N value of the recombinant components was slightly lower than that of the broad-leaved Korean pine forest.The determination coefficient of nitrogen to organic carbon in the group and recombination(especially light group)components is also higher than that of broad-leaved Korean pine forest.It indicated that the secondary forest of Populus euphratica distributed a higher proportion of organic carbon and nitrogen in the relatively nitrogen-rich recombinant components.