Degradation Process And Mechanism Of Alpine Swamp Wetland In The Source Of Yellow River Based On Soil Carbon And Nitrogen

Due to its cold climate,the soil organic matter decomposes slowly in alpine marsh wetland,which accumulates a huge amount of soil organic carbon(SOC)in a long time.In recent years,with climate warming and human disturbance,the degradation of alpine swamp wetlands has accelerated,and organic carbon has decreased.The wetland gradually succeeded to alpine meadows.Degradation of alpine swamp wetlands means that soil organic carbon is gradually disappearing,and carbon is released into the atmosphere in the form of greenhouse gases,which will cause the temperature to rise.Soil organic carbon and total nitrogen are important indicators to evaluate wetland soil quality and play an important role in the global carbon and nitrogen cycle.As a feature of alpine marsh wetlands,freeze-thaw mounds are mainly grass mounds with Kobresia tibetica above the water accumulation area.The low-lying land between the freezing and thawing mounds is called inter-mound,and the dominant species is Carex moorcroftii.In this study,the Dawutan alpine marsh wetland plot in Maqin County,Guoluo Prefecture,Qinghai Province was selected as the experimental site to study the soil organic carbon,organic carbon composition,humus,and microbial diversity of freeze-thaw mounds and between the grass patches in the alpine swamp wetland and the area of outer degraded wetland.In response to different degrees of degradation,at the same time,a variety of artificial restoration measures are set up to determine the effect of vegetation and soil restoration under different artificial restoration measures.The main results were as follows:1.Topsoil within 0-30 cm was the main distribution of soil organic carbon and nitrogen in alpine swamp wetland.There was a significant positive correlation between soil organic carbon and nitrogen contents.Soil water content at two kinds of patches was significantly correlated with soil organic carbon and total nitrogen(P< 0.01).With the degree of degradation in alpine swamp wetland,the water content,soil organic carbon and nitrogen contents,and carbon and nitrogen storages decreased.The descending speed of frozen-thawing patch was faster than that of between the grass patches.There was a significant negative correlation between the number of frozen-thawing patch and those of soil organic carbon/nitrogen contents and carbon / nitrogen storages.There was a significant positive correlation between the size of frozen-thawing patch and those of soil organic carbon/nitrogen content and carbon / nitrogen storage(P< 0.01).The results indicate that there are significant differences in soil carbon / nitrogen content and carbon / nitrogen storage among the different degrees of degradation in alpine swamp wetland.The soil water content,the number and frozen-thawing patch were indicative of soil carbon and nitrogen storage in alpine swamp wetland degradation.2.The relationship between the total soil organic carbon and total nitrogen in the alpine swamp wetland soil profile(0~200 cm)is: Non Degradation > Light Degradation > Heavy Degradation.The soil water content is positively correlated with soil organic carbon and total nitrogen(P <0.05).Soil organic carbon and total nitrogen are more sensitive to soil moisture with the deterioration of Alpine swamp wetland.Microtopography is closely related to the degree of wetland degradation,soil water content,soil organic carbon,and nitrogen,especially in the near surface layer of soil.These results indicate that there are significant differences in soil carbon / nitrogen content among the different degrees of degraded alpine swamp wetland.This result showed that SWC was an important indicator of SOC/TN in alpine swamp wetland.It is highly recommended to strengthen water injection into the wetland as a means of effective restoration to reverse alpine meadow back to alpine swamp wetland.3.The organic carbon components such as light fraction organic carbon,heavy fraction organic carbon,dissolved organic carbon and microbial biomass carbon,of frozen-thawing patch and between the grass patches decreased with the aggravation of degradation degree,and frozen-thawing patch within 0-10 cm was a significant difference(P < 0.05).The soil organic carbon components of frozen-thawing patches were more sensitive than that of between the grass patches.Heavy fraction organic carbon content is 32.46~160.22 g· kg-1,accounting for 94.83%~97.76% of soilorganic carbon,which is the most important component of soil organic carbon.With the aggravation of degradation degree,the proportion of microbial biomass carbon in frozen-thawing patch and between the grass patches decreased significantly(P < 0.05),and the proportion of soil microbial biomass carbon were sensitive to the degradation of alpine swamp wetland.There was significant correlation among soil organic carbon and light fraction organic carbon,heavy fraction organic carbon, dissolved organic carbon and microbial biomass carbon,and there was also significant correlation between each component(P < 0.01).In conclusion,the degradation of alpine swamp wetlands leads to a decrease in organic carbon components.The content and proportion of microbial biomass carbon can be used as key indicators to reflect the degradation of alpine swamp wetlands,and the content and proportion of heavy fraction organic carbon can be used as key indicators to reflect changes in soil organic carbon pools.4.The soil humus of the frozen-thawing patch and between the grass patches decreased with the degree of degradation.The humus carbon,humic acid and humic acid of the frozen-thawing patch were not degraded.The difference between light and severe degradation was significant(P<0.05),and grass patches are sensitive.In the composition of soil humus in the different degraded alpine swamp wetlands,HA/FA are all greater than 1,the degree of polymerization of soil humic substances is higher.The ratio of humic acid to fulvic acid in 0-10 cm soil of frozen-thawing patch patch presents a declining trend.The difference among non-degraded,lightly degraded,and severely degraded is significant(P<0.05).Soil water content and total nitrogen are positively correlated with soil humus,indicating that soil water and total nitrogen are the dominant environmental factors that limit soil humus in alpine swamp wetlands.The replenishment of surface water and nitrogen fertilizer should be strengthened in the restoration of alpine swamp wetlands.The cellobiohydrolase(CBH),?-1,4-xylosidase(BXYL),?-1,4-glucosidase(?G),?-1,4-glucosidase(BG),leucine peptidase(LAP),?-1,4-N-acetylglucosaminidase(NAG)and urease(UR)for humin and the formation of humic acid have a significant promoting effect in the frozen-thawing patch,and the enzyme activity and microbial biomass between the grass patches have a significant promoting effect on the formation of soil humus.5.The degradation severity changed the species composition of soil microorganisms at the level of OTUs,and the OTUs species of between the grass patches were more than that of frozen-thawing patch.The soil fungi OTUs species had changed significantly.The diversity indexes of bacteria(between frozen-thawing patch and between the grass patches)were higher than that of fungi.The dominant microbial species among the different degradation stages were the same.The dominant species of bacteria and fungiwere Proteobacteria and RB41,and Ascomycota and Mortierella,respectively.The abundance of dominant microorganisms between un-degradation and heavy degradation was significant different except RB41(P < 0.05).The dominant microorganisms of between the grass patches were more sensitive than that of frozen-thawing patches.It was found that the main factors affecting soil microbial community structure were soil water content,soil organic carbon,microbial biomass carbon,microbial biomass nitrogen and sedge coverage.Heavy degraded alpine swamp wetland could decrease the microbial diversity.So,the frozen-thawing patch and sedge species should be first protected,and the supplements of soil water content,soil organic carbon,microbial biomass carbon and nitrogen should be strengthened for alpine swamp wetland restoration.6.After principal component analysis,the soil index values of light degradation between the grass patches and heavy degradation are high,and the soil conditions are similar.The vegetation index values of the light degradation and heavy degradation are high,and the vegetation conditions are similar.The degradation of alpine swamp wetland is a succession process of interactions of multiple factors.Soil water content is the key factor affecting the degradation of alpine swamp wetland.Climate warming is the most important reason for the degradation of alpine swamp wetland.The indirect effect of micro-topography accelerates the study area.7.Through the treatments of sowing,fertilization,fertilization with sowing,the vegetation coverage,height,and aboveground biomass of degraded alpine swamps all showed an increasing trend,which shows that sowing and fertilization are beneficial to plant growth.The sowing and fertilization measures are more conducive to the increases of plant coverage and above-ground biomass.Too much or too small a sown amount is not conducive to plant growth,resulting in a decline in plant growth traits.From the perspective of conducive to plant growth.The planting rate of artificial vegetation in the alpine marsh wetland is more suitable for 3g/m2 and 30g/m2 for fertilization.The treatmnets of sowing,fertilization,fertilization and sowing make the total nitrogen content of the degraded alpine marsh wetland increase,but the total potassium content does not change significantly.After full P fertilization,the soil organic carbon increases,and the soil increases but it is not significant.Through comprehensive judgment,artificial vegetation establishment measures increased the content of soil organic carbon and improved soil properties.It can significantly inhibit the degradation of alpine marsh wetlands and achieve the purpose of protecting wetlands.