Soil Organic Carbon Storage And Distribution Characteristics In Xinjiashan Of Qinling Mountains

In order to study the soil organic carbon storage and the distribution characteristics in different forest types in Xinjiashan forest region of Qinling Mountains,soil samples of 0¹0cm,10²0 cm,20⁴0 cm and 40⁶0 cm in depth were collected to analyze the variations in soil organic carbon?SOC?,soil dissolved organic carbon?DOC?,microbial biomass carbon?MBC?and soil readily oxidizable carbon?ROC?under the forest types,the soil organic carbon content and organic carbon density of different forest types and different age class of the same forest type were analyzed,and the soil organic carbon storage was estimated by vegetation type method.The results were showed as followings:The distribution characteristics of active soil organic carbon under typical vegetation types of Xinjiashan forest:SOC in high altitude area was significantly higher than low altitude area,the content of SOC was Shrub>Piceaasperata>Betulaalbo-sinensis Burk along the whole soil profiles in high altitude area.SOC of larix is greater than the Quercusaliena var.acuteserrata in low altitude area.DOC and MBC in high altitude area were higher than low altitude area.The MBC contents of Piceaasperata and the ROC contents of Shrub were higher than other vegetation types in the same soil layer.The content of ROC is Shrub>Piceaasperata>Betulaalbo-sinensis Burk along the whole soil profiles in high altitude area.ROC of larix is greater than the Quercusaliena var.acuteserrata in low altitude area.The DOC/SOC ratio increased with increasing soil depth,while the ROC/SOC ratio decreased with increasing soil depth for all vegetation types.Nevertheless,the variations of MBC/SOC ratio along soil profile were different among various vegetation types.There were significantly positive correlations between SOC,DOC,MBC,ROC,total nitrogen?TN?and soil moisture content.The contents of soil organic carbon and active soil organic carbon were negatively correlated with soil bulk density and pH.The present study demonstrated that soil organic carbon in high altitude area was significantly higher than low altitude area,SOC in high altitude area is Shrub>Coniferous forest>Broadleaf forest along the whole soil profiles,SOC of Coniferous forest was greater than Broadleaf forest at the same altitude.The active fractions of soil organic carbon were under the combined effects of many various factors and they could quickly respond to the environmental changes and variations of soil organic carbon pool.Spatial distribution characteristics of soil organic carbon content in forest areas:through analysis of 65 soil samples covering the entire forest area,the soil organic carbon content in forest areas ranged from 3.97 to 37.71 g·kg^-1,and the average organic carbon content was17.30 g·kg^-1.The coefficient of variation of organic carbon content in all soil layers ranged from 39.87%to 58.16%,which was a moderate degree of variation.It was influenced by both structural factors and random factors.Trend surface analysis of soil organic carbon content showed a decreasing trend from west to east and an upward trend from south to north.The distribution map of soil organic carbon in the forest area showed that a gradual downward trend from northwest to southeast,and the northwest was larger than the southeast.The level of organic carbon content was expressed as:Jiucaipin Forest Farm>Yanwangbian Forest Farm>Xinjiaping Forest Farm>Donghe Forest Farm>Xiaoshuangou Forest Farm>Longwangmiao Forest Farm.The soil organic carbon content in the forest area had an obvious three-direction zonality?i.e.,longitude zonality,latitude zonality,and vertical zonality?,increases with increasing latitude and elevation,and decreases with the increase of longitude.However,the altitude was the most vital factor for the spatial variation of organic carbon in forest.The distribution characteristics of the soil organic carbon content in different forest types:forest soil organic carbon content ranged from 1.46±0.39 g·kg^-1 to 62.27±1.19 g·kg^-1,soil organic carbon?SOC?decreased with increasing soil depth,and there were significant differences among forest types,the average organic carbon content in young forests,middle-age forests,and mature forests of different forest types was the highest in the Cunninghamia and the lowest in the Pinus armadiifranch.The average soil organic carbon content was the highest in Shrubs,which was 37.50±0.25 g·kg^-1.The young forest of Pinus armadiifranch was only 4.00±0.43 g·kg^-1.The average soil organic carbon content of the same forest type increased with the increasing of the age.The distribution characteristics of the soil organic carbon density in different forest types:Soil organic carbon?SOC?density decreased with increasing soil depth,and there were significant differences between 0²0 cm and 0⁶0 cm soil layer,in which the soil organic carbon density ranged from 20.94±2.75 to 63.68±4.13 Mg·hm^-2 and 34.50±3.43 to 142.40±8.92 Mg·hm^-2,respectively.Soil organic carbon density of Pinus armadiifranch,Quercus forests,Birch forests,Soft wood,Hard wood increased with the increasing of the age,and soil organic carbon density of Cunninghamia and Larix forests increased first and then decreased.The soil organic carbon storage in Xinjiashan of Qinling Mountains:forest soil organic carbon stock ranged from 1.01±0.10 Gg to 482.53±54.76 Gg,soil organic carbon storage decreased with increasing soil depth.The amount of soil organic carbon storage in the 0²0cm and 0⁶0 cm soil layer in Xinjiashan of Qinling Mountains was 1052.81±52.44 Gg and2127.89±113.32 Gg,respectively,and the average density of soil organic carbon was 41.58Mg·hm^-2 and 84.05 Mg·hm^-2,respectively.The total organic carbon storage of Quercus forests and Birch forests was 1435.75±113.62 Gg,account for 67.47%of the total reserves of forest organic carbon,and with the largest contribution rate.The total organic carbon storage of the Mid-aged forest and Mature forest account for 96.28%of the forest soil total organic carbon storage.Relative to other forest stands,the indexes of soil organic carbon abundance of Cunninghamia,Larix forests and Shrubs was 1.43,1.35 and 1.69,respectively.Organic carbon absorption and storage capacity were the highest in forest.For soil organic carbon storage of Shaanxi Province,the indexes of soil organic carbon accumulation of Xinjiashan was 1.25,and the contribution rate of soil organic carbon was much higher than the average contribution rate regions of the Shaanxi Province.