| Wetlands are important natural resources for the survival and development of human society.Wetlands have important effects on storing carbon and nitrogen,regulating climate and water conservation,protecting species diversity,and maintaining regional ecological security.Qixing River Wetland?132°5?-132°26?E,46°40?-46°52?N?plays an important role in the ecological balance of wetlands in Heilongjiang Province and Northeast China.Wetland reclamation activities since the 1950s have drastically reduced the area of Qixing River Wetland and fragmented wetland landscapes.The project of returning farmland was implemented in 2002.According to the different terrains in the wetlands,natural recovery and artificial recovery were adopted in accordance with local conditions.The research site is located in the experimental area of the Qixing River Wetland National Nature Reserve.In 2017 and 2018,field sampling and indoor analysis were performed to analyze the carbon and nitrogen and phosphorus content and the characteristics of wetland soils and litter carbon,nitrogen,and phosphorus under diff-erent restoration methods.Decomposition and release of litter,and the relationship of carbon,nitrogen,and phosphorus between litter and soil were also analyzed.The main results are as follows:?1?Qixing River Wetland soil organic carbon?SOC?content was between 18.11g·kg-11 to 54.73 g·kg-1,total nitrogen?TN?content was 2.09 g·kg-1-3.89 g·kg-1,total phosphorus?TP?content was between 0.44 g·kg-11 to 1.91 g·kg-1.With the reference of the national soil carbon,nitrogen,and phosphorus content classification standards,the SOC content of wetland soil has reached Grade I and Grade II standards.The SOC nutrient status was better,the TN was in an excellent state,and the TP content was in the middle to upper to excellent state.In general,the SOC content of returning farmland to wetland was higher than that of natural wetland,which was beneficial to the restoration of vegetation growth.The TP content of soil in spring and summer was lower than that in autumn,which was related to the large demand for phosphorus by plants in the vigorous growth period.Nitrate nitrogen and ammonium nitrogen contents had a negative correlation trend,and the changes between seasons and wetlands reflected the characteristics that were beneficial to plant growth.In general,the variability of SOC and TN content in natural wetlands was relatively lower,indicating that the natural wetlands were relatively stable in carbon and nitrogen content and metabolism.The returning farmland to wetland was still in the recovery stage and the soil nutrients were in the dynamic adjustment stage.The variability of soil element content was small in autumn.Plants grew vigorously in spring and summer,and the metabolism of C,N,and P in the soil between plants and soil was active.The plant growth in the autumn entered the mature stage.The absorption of nitrogen was weakened,and the contents of C,N,and P in the soil tended to be balanced.?2?The C:N:P values of Qixing River Wetland soil was between 112:11.5:1?molar ratio?to 163:15:1,which was close to the average soil C:N:P?134:9:1?in China and carbon content appeared rich level.The change of the C:N:P value of the natural wetland from year to year was smaller than that of the converted wetland,which reflected the relative stability of the proportional relationship between the natural wetland C,N,and P.C:N values were lower than the national C:N?18.22?.The measurement ratio reflects that soil nutrient metabolism was to promote soil to increase effective nutrients.The C:P values ranged from 10.27 to 78.76,and the availability of phosphorus in wetlands was high.Among them,C:P was generally lower than that of natural wetlands and naturally restored wetlands under artificial restoration methods,reflecting that the restoration methods have increased the phosphorus effectiveness.N:P values were lower than the national level?13.60?.Wetland soils were restricted by N in terms of N and P supply.Among them,natural wetlands were more restricted by N,and smaller ones were naturally restored wetlands.The variability of carbon,nitrogen and phosphorus content and metering ratio of Qixing River Wetland was at a moderate level.The correlations of C:P,N:P in wetland soils in 2017 and 2018 were significant positive?P<0.01?,indicating that the metabolism and balance of C,N,and P in wetland soils were closely related.The degree of correlation between the metered ratios of C,N,and P elements in abandoned wetlands was weaker than that in natural wetland elements,which indicated that the relative stability of the interaction relationship between natural wetlands C,N,and P was relatively low.The interaction between N and P elements had a large variation,which had a certain relationship with the dynamic adjustment of nutrients in returning farmland to wetland.?3?Qixing River Wetland litter SOC and TN decomposition rate showed net release state,while TP is showed enrichment.The SOC released by litter decomposition had a significant effect on soil SOC accumulation,which was consistent with significant positive correlation between soil C:N and initial litter SOC content?P<0.01?.The increase rate of SOC in natural wetland soil was the highest,reaching 146.99%,which was coincided with significant positive correlation between the release of SOC from natural wetland litter and the increase in soil SOC?P<0.01?.The release of SOC from wetland litter in farmland was significantly positively correlated with the increase in soil SOC?P<0.05?.Among them,the increase rate of wetland SOC after returning farmland to restoration was 110.47%,and the natural restoration of wetland reached81.77%.The artificial restoration of poplar plantation recovered was more than natural vegetation.The soil SOC accumulated quickly,and the accumulation of wetland soil organic matter under different recovery methods was directly related to the return of litter.Nitrogen decomposition in litter was net release,and the net accumulation of TN in soil was not significantly changed,indicating that the source of nitrogen in soil depended not only on the return of litter decomposition,but also on the plant absorption,atmospheric nitrogen deposition,water conditions,soil structure,snow supply,ect.The accumulation of litter TP showed a phenomenon of phosphorus enrichment in naturally restored wetlands,which was higher than that of artificial restoration and natural wetlands.The change of phosphorus in litter had a certain relationship with the decomposition time.The monitoring of wetland litter TP in this study period is in the TP enrichment stage.?4?The variability of the litter C,N,P and C:N,C:P,N:P as well as C,N,P decomposition rates of Qixing River Wetland in the autumn of 2017 and spring of 2018ranged from weak to moderate variability.The catabolic balance of litter C and N is less affected by external conditions,which was consistent with the characteristics of lower variability of soil SOC content and C:N value.From the overall situation of changes in the content of carbon,nitrogen,and phosphorus in wetland soil,the variability of natural wetlands is small,which indicated that the dynamic change of wetland was relatively large.These results implied that wetland restoration still need long-term adjustment process to achieve the btter status. |
PDF Full Text Request