| There is a large area of tidal flat wetland in the lower reaches of Xiaolangdi reservoir of the Yellow River.As a result of the diversion of water and sediment from the reservoir and the oscillation of the Yellow River,part of the tidal flat is constantly submerged and exposed.At the same time,there are many different land types in this area because of the large amount of reclamation by coastal farmers.Wetland is the"source"or"sink"of nitrogen,as well as the"converter"of nitrogen.Nitrogen cycle of wetland occupies a very important position in the whole nitrogen cycle process,and the change of land type inevitably leads to the change of nitrogen cycle,which will lead to a series of ecological risks,such as the enhancement of greenhouse effect and eutrophication of water.Therefore,it is very important to study in this aspect.Four land types were selected in Henan Xinxiang Yellow River Wetland Birds National Nature Reserve:the seasonally submerged tidal flat without vegetation（GT1）,the seasonally submerged tidal flat with vegetation（GT2）,the farmland reclaimed from tidal flats（GT3）and the wetland which was greatly affected by human activities（GT4）.We combined the in situ field sampling and laboratory analysis,the spatiotemporal pattern of nitrogen among different land types was reflected by the seasonal variation and variance analysis of N2O emission flux and soil inorganic nitrogen concent,we also analyzed the correlation among N2O emission flux,soil inorganic nitrogen content and soil physicochemical factors interrelated in order to provide theoretical basis and data reference for Yellow River wetland management.The main results are as follows:（1）The N2O emission fluxes of the four land types all showed a seasonal variation trend showing that the minimum appeared in winter,and the maximum reached in summer with the increase of temperature and plant growth.Although N2O absorption occurs in all four land types in a whole year,it is mainly manifested in N2O emission.The N2O emission flux of farmland reclaimed from tidal flat is significantly higher than that in other plots（P<0.05）.Although there is a difference in N2O emission flux among GT1,GT2 and GT4,which has not yet reached a significant level（P>0.05）.（2）The seasonal variation of soil ammonium nitrogen content and nitrate nitrogen content among different soil layers at each point showed certain differences.The nitrate nitrogen content in GT1 and GT2reached its maximum value in spring,while GT3 and GT4 in summer.Among four land types ammonium nitrogen and nitrate nitrogen content of vertical distribution characteristics are different.Besides GT1,ammonium nitrogen and nitrate content in other three types of lands soil decreases with the increase of soil depth,at the same time,the soil NO3--N content of GT3 is always higher than that in GT1,GT2 and GT4,which reached significant level in all soil layers except in 20～30cm（P<0.05）.（3）Soil temperature of four land types changed seasonally,between 1.3℃～34.4℃.Soil temperature of GT1 and GT2 was generally higher than others.In GT1 and GT2,the soil VWC first decreased then increased with the deepening of soil depth,while in GT3 and GT4,the soil VWC increased with soil depth,and the soil VWC of GT3 is generally lower than other plots.The soil bulk density of GT3 is lower than that of GT1,GT2 and GT4.In different land types,soil bulk density showed different rules with the increase of soil depth,the farmland is lower than that of the other three land types.At the same time,cultivation influenced the soil nitrogen content and soil carbon-nitrogen ratio in the soil layer 0～20cm greatly.（4）Among the soil physical and chemical factors,soil temperature and soil moisture content are the main factors affecting N2O emission flux,which were positively correlated.In addition,the correlation between N2O emission flux and soil temperature in GT1 and GT2 reached a significant level（P<0.05）,and the correlation between N2O emission flux and soil VWC reached a significant level in GT3（P<0.05）.Land reclamation changed the relationship between the soil NO3--N content and soil NH4+-N content,soil bulk density and soil nitrogen components,in GT1,GT2 and GT4 the content of soil NO3--N and soil NH4+-N were showing a positive correlation relationship,a negative correlation relationship between soil bulk density and ammonium nitrogen,nitrate nitrogen,total nitrogen,but in GT3,there was a negative correlation between the two inorganic nitrogen components and a positive correlation between soil bulk density and soil nitrate nitrogen. |
