| As a typical estuarine delta wetland with rich biodiversity and high productivity,the Yellow River Delta coastal wetlands have been severely damaged in recent years due to strong human activities,and to curb the process of wetland degradation,the Yellow River Delta coastal wetlands have been implemented as a following and wetting project.To investigate the ecological restoration effect of the Yellow River Delta,this study takes the restored wetlands in the Yellow River Delta coastal wetlands with different years of following(2 a,3 a,4 a,6 a,11 a,15 a,and 16 a)as the research object,and uses natural wetlands and farmland as the control,and uses the spatial instead of a temporal method to analyze the evolution of soil,plant and seed bank in the Yellow River Delta coastal wetlands following area,and assess the study aims to provide a theoretical basis and scientific guidance for evaluating the ecological restoration effect of the Yellow River Delta coastal wetlands.The results of the study are as follows.(1)The soil bulk density of farmland is relatively low due to the influence of agricultural activities,with a soil bulk density of 1.13±0.00～1.27±0.01 g/m~3;the soil bulk density after restoring shows an overall decreasing trend with the increase of restoring years,and the soil bulk density of the 0～10 cm soil layer decreases from 1.45±0.01 g/m~3 to 1.12±0.02 g/m~3,but it is still higher than farmland overall.The soil moisture content of farmland is low,ranging from 6.34±0.06%to 14.70±0.54%,but after restoring,the soil moisture content increases with the increase of restoring years,from19.35±1.12%to 24.86±0.45%at 2 a to 24.56±0.84%to 34.86±1.02%at 16 a,and is close to the natural wetland level.Compared with the composition of soil particles in natural wetlands,the content of powder and grains is relatively high and the content of soil clay particles is relatively low in the restoring soil.In the same place,the deeper the soil layer,the greater the content of clay particles.The soils in the study area are all alkaline,with p H values greater than 7.The natural wetland soils are more alkaline,with soil p H values ranging from 8.39±0.03 to 8.91±0.04,while the agricultural soils are less alkaline due to human interference,with soil p H values ranging from 7.46±0.07 to7.99±0.06.Soil organic matter,total phosphorus,total nitrogen and ammoniacal nitrogen content showed an increasing trend with increasing years of restoring,with soil organic matter increasing from 4.66±0.07～6.58±0.02 g/kg at 2 a to 5.37±0.02～8.67±0.01g/kg at 16 a.Soil total phosphorus increased from 0.34±0.01～0.48±0.01 g/kg at 2 a to0.56±0.01～0.68±0.01 g/kg at 16 a,soil total nitrogen increased from 0.15±0.02～0.32±0.01 g/kg at 2 a to 0.56±0.01～0.92±0.01 g/kg at 16 a,soil ammoniacal nitrogen increased from 3.02±0.09～6.25±0.15 mg/kg at 2 a to 8.75±0.37～22.41±0.92 g/kg at16 a.The soil C/N and C/P ratios as a whole decreased with increasing years of restoring.C/N decreased from 20.30±0.6131.92±4.24 at 2 a to 9.43±0.15～9.53±0.14 at 16 a,C/P decreased from 13.47±0.19～14.47±0.60 at 2 a to 9.54±0.19～12.67±0.25 at 16 a,while the soil N/P ratio increased with increasing years of restoring,from 0.44±0.07～0.73±0.04 at 2 a to 1.00±0.03～1.34±0.01 at 16 a.The results of this study indicate that the wetland restoration project in the coastal wetlands of the Yellow River Delta can improve the soil physicochemical properties,and the longer the years of restoring,the closer the wetlands are to the natural wetland state.(2)With the increase of restoring years,plant species gradually increased from a single agricultural crop,and the importance value index of reed gradually increased and became the dominant species in the region;Simpson index and evenness index all showed an increasing trend,Simpson index increased from 0.18±0.01 at 2 a to 0.47±0.00 at 16a,evenness index increased from 0.06±0.00 at 2 a to 0.16±0.01 at 16 a.The plant carbon,nitrogen,phosphorus and potassium contents showed an overall decreasing trend with the increase of restoring years,the plant total carbon content decreased from 461.46±18.41g/kg at 2 a to 415.44±9.74 g/kg at 16 a,and the total plant nitrogen content decreased from 20.12±1.92 g/kg in 2a to 13.92±0.29 g/kg in 16 a,total plant phosphorus from1.08±0.00 g/kg in 2 a to 0.74±0.04 g/kg in 16 a,total plant potassium from 15.37±4.11 g/kg in 2 a to 12.28±0.38 in 16 a.The biomass and nutrient accumulation per unit area showed an increasing trend,with biomass increasing from 74.80±11.54 g/m~2 at 2 a to 198.40±6.16 g/m~2 at 16 a,biomass carbon increasing from 34.52±1.20 g/m~2 at 2 a to82.42±1.93 g/m~2 at 16 a,and biomass nitrogen increasing from 1.50±0.14 g/m~2 at 2 a to 2.76±0.06 g/m~2 at 16 a,and biomass phosphorus increasing from 0.08±0.00 g/m~2at2 a to 0.15±0.01 g/m~2,and biomass potassium increasing from 1.15±0.31 g/m~2 at 2 a to2.44±0.08 g/m~2;N/P and K/P showed an overall fluctuation with the increase in the number of years of restoring.N/P and K/P showed an overall fluctuating increase with increasing years of restoring,with N/K showing a trend of increasing and then decreasing,while C/N and C/P gradually increased.(3)As the number of years of restoring increased,the overall soil seed bank density tended to increase,from 900.00±70.71 seeds/m~2 at 2 a to 2462.50±88.39 seeds/m~2 at16 a;in the vertical direction,the seed bank density decreased as the soil layer increased,and the germination of species in the soil seed bank was mainly concentrated in the 0～10cm soil layer,with the deeper the soil layer,the lower the number of germinated seeds;the highest seed bank density was in the natural wetland,at 2562.50±17.68 seeds/m~2,and the lowest in the farmland,at 87.50±88.39 seeds/m~2.A total of eight species of plants belonging to five families and eight genera emerged from the soil seed bank in the study area,of which the family with the highest number of species was Gramineae;both Suaeda salsa and Calamagrostis pseudophragmites grew throughout the study area;the similarity index between the soil seed bank and the surface vegetation in the study area was low,all exceeding 0.5,and many surface plants did not appear in the soil seed bank.Many surface plants did not occur in the soil seed bank. |
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