Effects Of Water Level Regulation On Active Organic Carbon Components In Soil From A Peatland

Global warming,drought,and lowering of water levels caused by drainage have led to the 11% degradation of peatlands in the world,damaging the stability of the original carbon cycle process of peatlands.Water-level conditions are closely related to the formation and development of peatlands.It is the most important environmental element in the restoration of degraded peatlands and determines the mechanism and intensity of each key process of the carbon cycle.As a typical peatland in the Changbai Mountain area,the Baijiang River peatland has the functions of purifying water quality,regulating runoff,and improving microclimate and other ecosystem services.In the late 1980 s and early 1990 s,the local government conducted a project of wetland draining for forestation,providing an ideal environment for the study of the ecological function and restoration of the degraded peatland.In this study,we chose both the natural area and drainage area in the Baijiang River peatland as t our research objects.Through field in-situ monitoring and indoor water-level controlling experiments,we analyzed multi-proxies such as physical and chemical properties of the soil,active organic carbon components,and enzyme activities in the natural area and the drainage area,respectively,and revealed the change rule of soil active organic carbon component at different water levels.Additionally,choosing the water level condition,water content(SWC),soil p H,soil nutrient,and enzyme activity as environmental variables,we discussed the mechanisms of variations of the peatland soil active organic carbon component in the process of drainage and water level restoration.The main conclusions are as following:(1)The content of soil active organic carbon component and its distribution ratio changed significantly after the peatland was drained,and different active organic carbon components had different responses to drainage.The average soil organic carbon(SOC)and easily oxidized organic carbon(EOC)contents in the drainage area were 400.23 g/kg and68.27 g/kg,respectively,which were significantly higher than those in the natural area(378.55 g/kg and 61.68 g/kg).The content of soil microbial biomass carbon(MBC)in the drainage area was significantly lower than that in the natural area,and the difference was most significant at 0-80 cm(p<0.05).The soil soluble organic carbon(DOC)in the drainage area at 0-20 cm and 100-135 cm is significantly lower than that of the natural area,while the DOC content of the 50-100 cm soil was higher than that of the natural area(p<0.05).After draining of the peatland,both the conversion rate of soil SOC and the availability have decreased.The soil EOC distribution ratio(EOC/SOC)in the drainage area is higher than that in the natural area,while the soil MBC distribution ratio(MBC/SOC)is lower than that in the natural area.Drainage affects the stability of peatland soil SOC and is not conducive to the accumulation of soil SOC.The influencing factors of soil active organic carbon components under drainage were complex,including C/N ratio,total nitrogen(TN),polyphenol oxidase(PPO)and SWC.C/N,TN,and SWC were negatively correlated with soil DOC and positively correlated with other active organic carbon components,while PPO activity was positively correlated with soil DOC,and negatively correlated with other active organic carbon components.Different soil enzyme activities have different contributions to the soil organic carbon pool.The hydrolase β-1,4-N-acetylglucosamine glycosidase(NAG)has a great influence on the active organic carbon components of the soil in natural areas,while the oxidase PPO has the most significant impact on the active organic carbon component of soil in the drainage area.(2)Drainage reduces the stability of soil SOC.The changes of soil active carbon components after simulated drainage were consistent with those after field drainage,soil MBC content and its distribution ratio decreased,while the dynamic oxygen environment formed by water level fluctuations have a weaker impact on soil MBC than the static oxygen environment formed by continuous drainage.After the simulated drainage,the soil DOC content and its distribution ratio increased.Compared with drainage conditions,water level fluctuation conditions were more conducive to the release of soil DOC.Drainage affects soil microbial activity,and reduces soil SOC utilization and turnover rate.Soil SWC and hydrolase β-1,4-N-acetylglucosamine glycosidase(NAG)were the key factors affecting the change of soil active organic carbon components.Soil SWC was positively correlated with MBC content and its distribution proportion,but negatively correlated with DOC content and its distribution proportion(p<0.05).The hydrolase NAG was negatively correlated with EOC,MBC and its distribution ratio(p<0.05).The soil moisture content decreased and the activity of NAG enzyme was changed by drainage,which affected the dynamic change of soil active organic carbon(3)Restoration of water level is beneficial to improve the stability of soil SOC.After the simulated water level of the drainage area is restored,the content of MBC and DOC in 0-20 cm soil and their distribution ratio increase significantly,and the impact of water level restoration on soil MBC content is more significant than that of water level fluctuations.After the simulated water level was restored,the EOC content of 0-20 cm soil and its distribution ratio decreased significantly.Water level restoration increases the activity of microorganisms,promotes the utilization of soil SOC by microorganisms,and at the same time enhances the water solubility of soil SOC,reduces the oxidation rate of soil SOC,improves the stability of soil SOC,and facilitates the accumulation of soil SOC.In the simulation experiment of water level regulation in the drainage area,the soil oxidase PPO is the main factor affecting the change of active organic carbon components.There was a significant negative correlation between soil oxidase PPO and soil EOC content and its distribution ratio(p<0.05).Water level restoration can increase the activity of soil oxidase PPO and promote the organic decomposition of phenols,thereby affecting the soil EOC content.In the process of water level restoration,continuous flooding was more conducive to soil SOC accumulation than fluctuating conditions.The active organic carbon components and distribution ratios of soil in natural areas and drainage areas are significantly different.The changes in soil physical and chemical properties and enzyme activities caused by water level changes are the main factors affecting active organic carbon components in peatlands.This study is helpful to clarify the mechanism of degraded peatlands and the influence mechanism of water level changes on soil active organic carbon during the restoration process,and to deeply understand the relationship between soil oxidase-organic carbon component-hydrolase activity,which is the carbon of degraded peatlands.The improvement of sink functions provides a theoretical basis,and at the same time provides basic data and theoretical support for the assessment of the regional carbon budget of Changbai Mountain under the background of climate change.