| Increasing the concentration of atmospheric CO2leads to a series of serious environmental problems, the study of the carbon cycle has received the unprecedented attention. Middle-high latitude forest ecosystem in the eastern part of northeast China locates in the sensitivity region of the global change, plays an important role in maintaining regional ecological environment, and becomes the key region of carbon cycle research. Simulation of carbon cycling using the model is an important method for carbon cycle research. The Integrated Biosphere Simulator (IBIS) model is a useful tool for forest carbon cycle simulation, represents the development direction of the global carbon cycle model. Modeling carbon cycle in forest ecosystem in the eastern part of northeast China using the IBIS model is of great significance to the research of the terrestrial carbon cycle and global change.In order to make the IBIS model better reflect the spatial heterogeneity of carbon cycling and apply to simulate carbon cycle at the catchment scale in the east part of northeastern China, the study had improved IBIS model by integration of geographical information system (GIS), database, and Visual C#. Carbon cycling of the five forest types in the Zhangjiagou catchment of Heilongjiang province in northeast China was then simulated in2004using the improved IBIS model. The model was driven by meteorology, topography, vegetation and soil data. The simulated values were validated with measurements and other model simulation data, and the temporal-spatial patterns of carbon flux, its response to topographic factors were analyzed. The main results and conclusions were as follows:(1) Improved the IBIS model. The IBIS model can only simulate discrete plot, can’t simulate continuous vegetation spatial, and didn’t take into account the effects of topography on soil water flow and solar radiation, so the mechanism of forest carbon cycle simulation was imperfect. Therefore, GIS technology was applied, the catchment scale was selected, redistribution module of soil water and calculation module of solar radiation received by ground surface were modified, terrain analysis module was added, eight plant functional types for east part of northeastern China were sifted, phenology algorithm and model parameters were modified, the programming language and the data storage format of the IBIS model were optimized in this study. The improved IBIS model may simulate carbon and water process of continuous vegetation at the catchment scale in detail, reflect fully the spatial heterogeneity of forest carbon cycle under different terrain, provide useful tools for the simulation of carbon cycle in forest ecosystem at the catchment scale, and lay a solid foundation to the study of the regional carbon cycle simulation at large scale which basic unit was the catchment.(2) Achieved operation system of the IBIS model. By using Visual C#and Visual FoxPro database technology, the graphics interface operation system of the IBIS model was achieved in the study. The major functions of the system include:model input parameters reading, editing and management, the model simulation, model output settings, reading and exporting, and the system error prompting, etc. Overall, the system has the advantages of clear structure, beautiful interface, and good convenience in use.(3) Validated the IBIS model. The simulated soil respiration and net primary productivity of the IBIS model were compared with the measured data. The results showed that the improved IBIS model which had better simulated effect and reliable simulated results can be applied to simulate carbon cycle at the catchment scale in the east part of northeastern China.(4) Simulated soil respiration. The annual mean soil respiration was571gC/(m2·a) in the Zhangjiagou catchment. The spatial pattern of the annual soil respiration was similar to the spatial pattern of soil respiration for the growing season, which showed that high values of soil respiration were distributed in the north, southwest and southeast of the catchment, and the low values were largely in nearby valleys. The spatial pattern of soil respiration was closely related to topography, vegetation and other factors. During the growing season, the five forest types showed a similar seasonal pattern in simulated soil respiration, characterized by a mono-peak curve, with a summer maximum and an early and late growing season minimum. The peak soil respiration value of the five forest types occurred in July. Mixed deciduous forest was146.3gC/m2, and Larch plantation was85.5gC/m2. The total amount soil respiration was865.44tC/a in the Zhangjiagou catchment in2004. Among the different forest types, the mixed deciduous forest had the largest area of the study region, the highest annual mean soil respiration (628gC/(m2·a)) and its total amount was486.39tC/a, while the Larch plantation had the smallest area of the study region, the lowest one (356gC/(m2-a)) and its total amount was0.29tC/a. In the growing season, the simulated soil respiration of the five forest types showed a significant index correlation (P<0.001) with the simulated soil temperature at5cm depth, and could explain approximately70%of the seasonal variation in soil respiration. There was no obvious correlation between the simulated soil respiration and the simulated soil moisture for all forest types at5cm depth. Among the topographic factors, the slope and aspect on soil respiration is greater than the effects of altitude on soil respiration, which was directly related to lower elevation in the study area.(5) Simulated NPP and NEP. The annual mean NPP of forests was375gC/(m2·a) in the Zhangjiagou catchment. The spatial pattern of NPP of forests generally presented that northeast and northwest area had the high values, and then gradually decreased in the central valley parts. During the growing season, the spatial pattern of NPP of forests in different month changed significantly. Seasonal variation of NPP of forests was closely related to the temperature, precipitation and solar radiation, etc. The variation of the monthly mean NPP characterized by a double-peak curve, and the peak value appeared in May and August. The total amount NPP of forests was541.72tC/a in the Zhangjiagou catchment in2004. Among the different forest types, the aspen-birch forest had the highest annual mean NPP (405gC/(m2·a)), while the mixed deciduous forest had the lowest one (336gC/(m2·a)). From relationship between NPP of forests and climatic factors, the correlation between the NPP and precipitation (R2=0.6657. P<0.01) was higher than the temperature (R2=0.5383. P<0.05). So the precipitation was the main limiting factors of determining NPP of forests in the Zhangjiagou catchment. Among the topographic factors, the altitude and slope had little effect on NPP of forests, while the aspect exerted significant impact on NPP of forests. Furthermore, NPP of forests on sunny slope was41%higher than that on shady slope.The annual mean NEP was93gC/(m2·a) in the Zhangjiagou catchment. The southeast region was the lowest NEP, and the central area was relatively higher NEP. The total amount of NEP was541.72tC/a in the Zhangjiagou catchment. The Aspen-birch forest and the Mixed deciduous forest had the largest area, those total amount of NEP accounted for about58%of the total NEP in the study region. Among the five forest types, the Larch plantation had the highest annual mean NEP (142gC/(m2·a)) and the strongest carbon sink, while the mixed deciduous forest had the lowest one (22gC/(m2·a)) and the weakest carbon sink. |
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