| In the backdrop of the climate change,forest soil organic carbon had been focused in the study of the global carbon cycle.Not only plant composition and structure but also soil organic carbon would change in the process of vegetation succession.The soil physical and chemical properties,aggregates,soil organic carbon and its components,organic carbon structure and stability of evergreen broad-leaved forest and Cunninghamia lanceolata forest,Cryptomeria fortunei forest and coniferous and broad-leaved mixed forest unde the same site condition and vegetation succession time were researched systematically to acquire the impact mechanisms of different forest stand types on soil organic carbon in the national nature reservation of Fengyang Mountain.The goal of study was to provide scientific basis for policy-making of tackling climate change,forest management and so on.The results showed:(1)On the whole,content of soil organic carbon of evergreen broad-leaved forest was the higher than that of Cunninghamia lanceolata forest.That of Cryptomeria fortunei forest was the higher than that of coniferous and broad-leaved mixed forest.Contents of readily oxidized carbon of evergreen broad-leaved forest which were 1518.47 and 786.63 mg/kg in the 0-20 cm and 20-40cm layers respectively were the higher than those of Cunninghamia lanceolata forest respectively(P<0.05).Contents of readily oxidized carbon of Cryptomeria fortunei forest which were 1342.36and 540.35 mg/kg in the 0-20 cm and 20-40cm layers respectively were the lower than those of coniferous and broad-leaved mixed forest(P<0.05).On the whole,Contents of readily oxidized carbon were the highest in summer while were the lowest in winter.Contents of recalcitrant organic carbon of evergreen broad-leaved forest which were 2.23 and 1.60 g/kg in the 0-20 cm and20-40 cm layers respectively were the higher than those of Cunninghamia lanceolata forest(P<0.05).Contents of recalcitrant organic carbon of Cryptomeria fortunei forest which were 2.36and 1.31 g/kg in the 0-20 cm and 40-60 cm layers respectively were higher than those of coniferous and broad-leaved mixed forest(P<0.05).Contents of soil organic carbon,readily oxidized carbon and recalcitrant organic carbon showed the decreasing trends along the soil depth.(2)The>2 mm soil aggregates the proportions of which were 69.98%-77.74%were the dominant in soil.Compared with Cunninghamia lanceolata forest,mean mass diameters of soil aggregates of evergreen broad-leaved forest increased by 4.98%and 6.86%respectively in 0-20cm and 20-40 cm layers.Those of Cryptomeria fortunei forest were the higher than coniferous and broad-leaved mixed forest.Compared with Cunninghamia lanceolata forest,geometric mean diameters of soil aggregates of evergreen broad-leaved forest increased by 8.41%and 15.05%respectively in 0-20 cm and 20-40 cm layers.Compared with coniferous and broad-leaved mixed forest,geometric mean diameter of soil aggregates of Cryptomeria fortunei forest increased by9.23%in 0-20 cm layer.The fractal dimensions of soil aggregates of evergreen broad-leaved forest which were the lower than those of Cunninghamia lanceolata forest were 2.00,2.09 and 2.01respectively in 0-20 cm,20-40 cm and 40-60 cm layers.The fractal dimensions of coniferous and broad-leaved mixed forest which were the higher than those of Cryptomeria fortunei forest were2.08 and 2.12 respectively in 0-20 cm and 40-60 cm layers.The>2 mm soil aggregates,mean mass diameters and geometric mean diameters showed the decreasing trends along the soil depth,however the fractal dimensions showed increasing trends.Contents of soil organic carbon,readily oxidized carbon and recalcitrant organic carbon of soil aggregates in 0-20 cm and 20-40 cm layers of all forest types showed increasing trends along with decreased aggregate size.Contents of soil organic carbon,readily oxidized carbon and recalcitrant organic carbon of soil aggregates in 0-20cm layer were the higher than the same size aggregates in 20-40 cm layer significantly.Contents of soil organic carbon,readily oxidized carbon and recalcitrant organic carbon of soil aggregates of evergreen broad-leaved forest were the higher than the same size aggregates of Cunninghamia lanceolata forest mainly.Contents of soil organic carbon and recalcitrant organic carbon of soil aggregates of Cryptomeria fortunei forest were the higher than the same size aggregates of coniferous and broad-leaved mixed forest mainly.(3)In 0-20 cm,20-40 cm and 40-60 cm soil layers of different forest types,soil bulk density and pH value were 0.71-0.91 g/cm~3 and 4.43-5.14 respectively,and contents of total nitrogen,available phosphorus and available potassium were 1.05-3.11 g/kg,6.01-8.35 mg/kg and 88.08-161.94 mg/kg respectively.Soil bulk density and pH value showed the increasing trends along the soil depth,however contents of total nitrogen,available phosphorus and available potassium showed the decreasing trends.The soil organic carbon had significantly negative correlations with soil bulk and pH value,but positive correlation with total nitrogen,readily oxidized carbon,recalcitrant organic carbon and mean mass diameter.The readily oxidized carbon had significantly negative correlations with pH value,but positive correlation with total nitrogen and recalcitrant organic carbon.The recalcitrant organic carbon had significantly negative correlations with soil bulk and fractal dimension,but positive correlation with total nitrogen,readily oxidized carbon,available potassium,mean mass diameter and geometric mean diameter.The total nitrogen was leading factor influencing soil organic carbon.The soil organic carbon was leading factor influencing readily oxidized carbon.The soil organic carbon and fractal dimension were leading factor influencing recalcitrant organic carbon.(4)Compared with Cunninghamia lanceolata forest,alcoxyl carbon in soil organic carbon of evergreen broad-leaved forest was the higher,while alkyl carbon,aromatic carbon,alkyl carbon/alcoxyl carbon and hydrophobic carbon/hydrophilic carbon were the lower,implying that the stability of soil organic carbon of evergreen broad-leaved forest was poorer.Compared with coniferous and broad-leaved mixed forest,the alkyl carbon,alkyl carbon/alcoxyl carbon and hydrophobic carbon/hydrophilic carbon in soil organic carbon of the Cryptomeria fortunei forest were the higher,while alcoxyl carbon was the lower,implying that the stability of soil organic carbon of Cryptomeria fortunei forest was better.Compared with the 0-20 cm soil layer,the alcoxyl carbon in soil organic carbon of the 20-40 cm soil layer of different forest stand types decreased significantly,while the alkyl carbon,alkyl carbon/alcoxyl carbon and hydrophobic carbon/hydrophilic carbon increased significantly,implying that the stability of soil organic carbon in the 20-40 cm soil layer was better.With the increase of aggregate size,the alkyl carbon,alkyl carbon/alcoxyl carbon and hydrophobic carbon/hydrophilic carbon in organic carbon of soil aggregates showed decreasing trends,while the alcoxyl carbon showed increasing trends,implying that the stability of soil organic carbon combined in aggregates gradually turned to be poor.The comprehensive result indicated that the structure and stability of soil organic carbon in the study area were decided mainly by plant composition and structure of different forest stand types.(5)In the 0-20 cm layer,The contents of soil microbial biomass carbon and dissolved organic carbon of evergreen broad-leaved forest(707.60 mg/kg and 301.74 mg/kg respectively)were the higher than those of cunninghamia lanceolata forest(582.53 mg/kg and 208.30 mg/kg respectively)significantly(P<0.05).Those of cryptomeria fortunei forest(678.71 mg/kg and 316.33 mg/kg respectively)were the higher than those of coniferous and broad-leaved mixed forest(626.05mg/kg and 269.40 mg/kg respectively)significantly(P<0.05).At 10?,the content dynamics of microbial biomass carbon of various stand types were fast decline early and slow decline later,and the content dynamics of dissolved organic carbon were rising early but declining later.At 20?,the content dynamics of microbial biomass carbon and dissolved organic carbon of various stand types showed slow decline relatively.At 30?,the content dynamics of microbial biomass carbon under various stand types were rising early but declining later,and the content dynamics of dissolved organic carbon were fast decline early and slow decline later.At the same detection time,the contents of microbial biomass carbon of the same stand type were characterized by30?>20?>10?,and the contents of dissolved organic carbon were characterized by10?>20?>30?.At the same temperature,microbial biomass carbon and dissolved organic carbon of evergreen broad-leaved forest and coniferous and broad-leaved mixed forest on the whole were easier volatility than cunninghamia lanceolata forest and cryptomeria fortunei forest respectively. |
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