Effects Of Draining For Forestation On Carbon Source Or Sink Of Temperate Marsh Wetlands In Xiaoxing’ Anling Of China

The carbon （CO₂ and CH₄） emission fluxes, vegetation net primary productivity and carbon sequestration were studied by using static chamber gas chromatography method and Multi N/C 3100, HT 1300 Solids Module （Analytik Jena AG, Germany） and the relative growth equation method from natural marsh wetlands and Larix plantation-marsh swamps under different draining treatment （10 years,30 years） in Xiaoxing’anling of China, so as to evaluate the effects of draining for forestation on carbon source or sink of temperate marsh wetlands which based on net ecosystem carbon balance. The results showed that:（1） Draining for forestation were changed seasonal variation trend of CH₄ emission fluxes from natural marsh wetlands, which turn from approximate unimodal type into the emission and uptake appearing alternately. They were also changed the CH₄ source or sink function (From strong CH₄ emission source (annual fluxes were 155.928 kg·hm^-2·a^-1 from natural marsh wetlands) to weak CH₄ uptake sink (annual fluxes were-0.613,-0.350 and -0.964 kg·hm^-2·a^-1 from 10 years drainage ridge and ditch,30 years drainage ditch respectively) or weak CH₄ emission source (annual flux was 0.350 kg·hm^-2·a^-1 from 30 drainage ditch)).At the same time, draining for forestation were changed the main controlling factors of CH₄ emission from natural marsh wetlands soil. CH₄ emission fluxes from natural marsh wetlands and 30～40 cm soil temperature were significant positive correlation, but they were not related with 30～40 cm soil temperature after draining for forestation 10 or 30 years through growing season.（2） Draining for forestation did not changed the seasonal variation trends of CO₂ emission fluxes from natural marsh wetlands （They were both took on approximate bimodal pattern）. But the CO₂ annual emission fluxes were significantly decreased by 54.8% and 35.4%（P<0.05） from 10 and 30 years drainage ditches soil (7.64～10.91 t·hm^-2·a^-1), yet it (23.83 t·hm^-2·a^-1) was significantly increased by 41.1%（P<0.05） from 30 years drainage ridge soil. At the same time, draining for forestation were changed the main controlling factors of CO₂ emission from natural marsh wetlands soil. CO₂ emission fluxes from natural marsh wetlands soil and air temperature、0～30cm soil temperature were significant positive correlation, but that from 10 or 30 years drainage ridge and air temperature、0～40 cm soil temperature all were significant positive correlation, while that from 10 years drainage ditches were not related with air temperature and soil temperature,30 years drainage ditches and air temperature、0cm soil temperature were significant positive correlation through growing season.（3） The vegetation net primary productivity(15.44 t·hm^-2·a^-1) and annual net carbon sequestration (6.74 tC·hm^-2·a^-1) of natural marsh wetlands were significantly reduced by 31.9% and 30.6%（P<0.05） after the draining for forestation 10 years (10.51 t·hm^-2·a^-1 and 4.68 tC·hm^-2·a^-1), but there were no significant difference between larch plantation swamps and natural marsh wetlands （-6.7% and -5.2%, P>0.05） after the draining for forestation 30 years (14.40 t·hm^-2·a^-1 and 6.39 tC·hm^-2·a^-1).（4） There were no significantly effects of draining for forestation on annual soil net carbon emission from natural marsh wetlands (Natural marsh wetlands were reduced by 15% after the draining for forestation 10 years （P>0.05）,and they were increased by 11.5% after the draining for forestation 30 years, （P>0.05）.The carbon sink of natural marsh wetlands (2.08 tC·hm^-2·a^-1) were significantly decreased by 65.4%（P<0.05） after the draining for forestation 10 years (0.72 tC·hm^-2·a^-1), yet there were no significant gap between the larch plantation (1.20 tC·hm^-2·a^-1) and natural marsh wetlands （-42.3%, P>0.05） after the draining for forestation 30 years.Therefore, draining for forestation significantly were decreased the carbon sink of natural marsh wetlands at first 10 years and their were recovered as same as natural marsh wetlands after later 30 years.