| Wetland ecosystem is one of the most important carbon pools on earth.It play an important role in global carbon cycle,and climate change mitigation.However,two issues are still not sovled.Firstly,the spatial heterogeneity always results in uncertainty in carbon storage estimation at large scales.Secondly,wetlands not only sequestrate CO2 from atmosphere,but also emit CH4 to it,so this may result in wetlands to be a carbon sink or a source of atmospheric greenhouse gases,and this question is not still better understood due to the lack of comparing researches.Xiaoxing'anling is the main distribution area of forested wetlands in China and the sensitive area of global warming.But,there is still lacking carbon storage data of various forested wetland types.This will affect the accurate estimation of wetland carbon storage and the effectiveness of carbon storage management in this region.At the same time,the carbon source/sink of the forested wetlands also not be well understood,due to the lack of simultaneous measurement of CH4 and CO2.In view of these two problems,this study selected five typical temperate forested wetland types(alder swamp,white birch swamp,larch swamp,larch fen,and larch bog)in Xiaoxing'anling as research objects.The study(1)estimated the ecosystem carbon storage of each forested wetland type based on vegetation carbon storage and soil organic carbon storage(50cm depended on active layer depth).(2)And calculated soil carbon emissions by simultaneously measuring soil CO2 and CH4 emissions,then evaluated quantitatively the carbon sink function of each type based on soil carbon emission and NPP,and the specific role in the process of atmospheric warming according to the ecosystem cooling effect.The results showed that:(1)The vegetation carbon storage ranged from18.92±1.62 to 47.84±3.38 tC·ha-1,and showed the change trend of white birch swamps and larch fens>larch swamps and larch bogs>alder swamps.The spatial difference of vegetation carbon storage was mainly affected by biomass rather than vegetation carbon content.The mean water table and water table range in growing season had significant effects on vegetation carbon content and carbon storage of five forest wetlands.Water table range was the key factor affecting biomass,while mean water table was the key factor affecting vegetation carbon content.(2)The soil organic carbon storage ranged from 326.04±1.02 to 400.98±10.97 tC·ha-1,and it showed a regularity that the larch fens and larch bogs lay at permanent flooded habitats were higher than the other three wetland types lay at seasonal flooded habitats.The mean water table and water table range in growing season can significantly affect the soil bulk density and organic carbon content,but due to work in opposite directions,the direct influence of moisture factors on soil organic carbon storage was limited.(3)The ecosystem carbon storage ranged from 344.96±2.25 to 448.82±14.35 tC·ha-1.With larch fens as the highest,larch fens and white birch swamps were higher,but larch bogs is slightly higher than white birch swamps,alder swamps and larch swamps were the lowest.It showed a regularity that the larch fens and larch bogs lay at permanent flooded habitats were higher than the other three wetland types lay at seasonal flooded habitats.The distribution pattern of ecosystem carbon storage of 5 forested wetland types were basically the same,with soil carbon storage accounting for an absolute dominant position,and vegetation carbon storage occupying only a secondary position.(4)Soil carbon emission ranged from 3.83±0.70 to 4.37±0.28 tC ha-1·yr-1,while soil CO2 emission and soil CO2-C emission ranged 13.60±2.28 to 15.52±1.40t ha-1·yr-1 and 3.71±0.62 to 4.23±0.38 tC ha-1·yr-1,respectively,and there were no significantly differences among forested wetlands.But soil CH4 and CH4-C emission ranged from 0.001±0.001 to 0.67±0.33 t ha-1·yr-1 and 0.0004±0.0001?0.50±0.25 tC ha-1·yr-1,respectively,showing a decreasing trend with the elevation rising.Although the increase of CH4 emission had no significant effect on soil carbon emission,it can cause a significant increase of soil CO2 equivalent flux.The CO2 flux of alder swamps,white birch swamps and larch swamps had the strongest correlation with the temperature of the 5cm soil depth,the CO2 flux of larch fens and larch bogs had the strongest correlation with 10cm or 15cm soil depth temperature,respectively;CH4 flux of alder swamps and white birch swamps had the strongest correlation with 40cm soil layer depth temperature,while CH4 flux of larch bogs was mainly inhibited by surface temperature.(5)The NPP ranged from 4.93±0.15 to 9.92±2.40t ha-1·yr-1 or 2.27±0.07 to 4.50±1.09 tC ha-1·yr-1,and dominated by canopy layer(67.6%to 78.0%and 68.5%to 81.0%).The net carbon budget showed that alder swamps was carbon source(-2.10±0.21 tCha-1·yr-1),while other four forested wetland types were carbon sinks(0.14±0.05 to 0.60±0.29 tC ha-1·yr-1).Moisture factor had no significant effect on the carbon emission of forested wetlands,but it can affect the NPP and then change the carbon sink intensity.Ecosystem cooling effect showed that alder swamp had a strong promoting effect in atmospheric warming process,while white birch swamp had a slight promoting effect,and the other three forested wetlands had a slight mitigating effect in it.In this paper,the ecosystem carbon storage and carbon sink of temperate forested wetlands was estimated in Xiaoxing'anling,northeast China.and the influence mechanism of moisture factors on carbon storage was revealed.At the same time,the carbon sink function and ecosystem cooling effect were quantitatively evaluated.The research shows that improving vegetation productivity is a more effective way to enhance carbon sinks in temperate forested wetlands than controling soil greenhouse gas emissions.And protection and management of soil carbon pools should be concentrated to avoid the release of soil carbon from the perspective of maintaining the long-term carbon sink function of forested wetlands.This study is not only helpful to accurately estimate the carbon storage and carbon sequestration capacity of forested wetlands in China,but also has practical significance for effectively manage the carbon pool of temperate forested wetlands. |
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