| Forest soil labile organic carbon is not only an important indicator in revealing a regional carbon active, but also an important factor in measuring carbon stability. Organic carbon stability reacts the ability to resist the interference, i.e., the reaction soil ability of carbon "source" or "sink". Strong function coupling mechanism was found between forest soil carbon and nitrogen. Forest carbon and nitrogen influence each other and determine the forest ecosystem carbon cycle and carbon balance of the whole. Therefore, study on the changes of soil organic carbon and nitrogen components can explain the change of soil carbon and nitrogen pools in response to climate change. In this study, we chose deciduous broadleaved forest (BF,2730～2761 m), coniferous and broad-leaved mixed forest (TF, 2755～2854 m), coniferous forest (CF,3111-3430 m) and shrub forest (SF,3517～3564 m) four typical vegetation types which wear located in shady slope of the Western Sichuan Wolong Nature Reserve subalpine as the research objects, by the means of regular sampling surveys and analysis of the soil organic carbon and nitrogen components and physical and chemical properties, in order to research:(1) regulation of soil total organic carbon, labile organic carbon and nitrogen change in altitude and their mutual relations; (2) changes of soil organic carbon and nitrogen fractions under different vegetation types; (3) soil organic carbon stability differences in different altitude vegetation types. Finally, to reveal the subalpine forest soil carbon and nitrogen distribution characteristics and influencing factors, to provide basis and reference for the subalpine forest soil carbon and nitrogen pools of prediction and evaluation and carbon and nitrogen cycle feedback mechanism under the conditions of climate change in the future. The main results are summarized as follows:(1) The mean content of soil surface (0-20 cm) organic carbon in four vegetation types is 97.99 g/kg; soil organic carbon density is averaged 171.04 t/hm2, both wear increased significantly along with the increasing altitude, the amount of carbon was easily accumulated in high altitude.Content of organic carbon was increased first and then decreased in amplitude, the maximum is TF to CF on 23%, moreover, there is no significant differences between BF, TF two types above altitude 3111m and CF, SF below 2854 m, but BF, TF and CF, SF showed significant differences.(2) The mean content of soil dissolved organic carbon is 83.41 mg/kg (ranged from 59.69 to 113.89 mg/kg), content of microbial biomass carbon is 118.96 mg/kg (range from 82.87 to 1.4519 mg/kg), both wear increased first and then decreased along the altitude increasing, elevation is a significant factor on them, the content in TF forest is the highest than the others. Light fraction organic carbon average content is 65.58 g/kg (ranged from 38.17 to 91.83 g/kg), particulate organic carbon average content is 43.18 g/kg (ranged from 32.24 to 53.90 g/kg), easy oxidation organic carbon average content is 34.4 g/kg (range from 26.24 to 39.91 g/kg), each of the proportional distribution was in more than 30% making good contribution to soil organic carbon and can be as an indicator of carbon pool dynamics. Significant linear relationship was found in these three labile carbon fractions showing the sources of similar. Labile organic carbon fractions wear obviously differente in four vegetation types. Soil physical properties (pH), elevation and vegetation types wear significantly in influencing carbon dynamics.(3) Total nitrogen content is between 5.14-6.18g/kg, on average of 5.45 g/kg. Alkali hydrolyzable nitrogen (432.12 mg/kg), inorganic nitrogen (43.59mg/kg), dissolved organic nitrogen (13.96 mg/kg), microbial biomass nitrogen (13.87 mg/kg):all of them wear significantly decreased with the altitude increasing, elevation is one of the key factors of nitrogen components. Biological factors like vegetation types, diameter at breast height, coverage, and biomass of stem wear significantly correlated with available nitrogen contents. Soil physical properties affect the nitrogen content and distribution too.(4) Microbial biomass carbon and nitrogen ratio was significantly affected by soil organic carbon and nitrogen ratio, both of them wear significantly influenced by altitude and vegetation types, BF, TF and CF, SF showed significant differences. In this study, microbial biomass carbon and nitrogen ratio and soil organic carbon and nitrogen ratio increase along with the altitude increasing was found. Microbial biomass carbon and nitrogen ratio, soil carbon and nitrogen ratio and labile organic carbon and nitrogen wear significantly correlated in elevation, indicating the interaction of carbon and nitrogen, and different altitude of vegetation and soil carbon and nitrogen function coupling response mechanism are differently.(5) Surface soil organic carbon stability evaluation results in four vegetation types: stability of BF vegetation was the highest, while SF was the lowest, followed by SF<CF<TF<BF. It shows that soil carbon stock and activity of shrubland ecosystem in high altitude wear the hightest and may from now on carbon sink into carbon source under the conditions of future climate warming.In conclusion:the research area is an important carbon pool storage zone with its big soil organic carbon storage and high quality, and also an important potential carbon source with its hign active organic carbon pool allocation proportion; biological factors (vegetations, diameter at breast height, and biomass of stem) and abiotic factors (altitude, soil physical and chemical properties) affect the content and distribution of soil organic carbon; the organic carbon and nitrogen of forest soil interact with each other through a certain coupling mechanism to determine the dynamics of carbon pool of forest ecosystems. |
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