Study On Characteristics Of Soil Seed Bank And Its Vegetation Restoration Potential In Typical Rocky Mountainous Area Of North China

The Songshan area belongs to the rocky mountainous area of North China is a typical,ecologically fragile area,characterized by sparse vegetation and poor soil with a high concentration of gravel.At the same time,as location of Beijing 2022 Winter Olympics and Winter Paralympics Yanqing Competition Zone,construction and operation of relevant venues and supporting facilities will inevitably have an impact on the natural landscape and ecological environment.In this case,the use of SSB for local ecological restoration and landscape reconstruction have become one of the necessary options.In order to explore the ecological restoration potential of the SSB in Songshan area and improve the utilization efficiency of stripped topsoil,this study took the SSB under typical vegetation communities as the research object,carried out a long-term and comprehensive sampling survey,and summarized the characteristics of the SSB in Songshan area.On this basis,the influence and mechanism of the SSB by the aboveground vegetation,soil environment and topographic conditions were explained.By carrying out the long-term storage test of stripped topsoil and the vegetation restoration test,a more reasonable storage and utilization method of stripped topsoil was explored,and to provide theoretical basis and technological support for the stripping and utilization of topsoil in similar areas.The main conclusions of this study are as follows:(1)The characteristics of SSB in Songshan area showed significant spatial and temporal heterogeneity.The density of SSB of spring(April),summer(July)and autumn(October)were 1633–4933 grasins/m~2,833–2367 grasins/m~2 and 1233–2933grasins/m~2,respectively.The number of species was 133,88 and 116,of which herbs account for nearly 90%,and shrubs,semi-shrubs,vines,and trees were very few in the SSB.The density and richness of SSB were significantly affected by elevation and seasonal changes,and showed a trend of first decreasing and then increasing.The density and richness of the SSB decreased gradually with the increase of elevation,and the lowest value appeared in the area above 2000m.The SSB in the 0–10cm soil layer dominated the changes in the characteristics of the SSB in the study area,and concentrated more than 85%of the SSB,including more than 95%of the plant species in all SSB.(2)The similarity between aboveground vegetation and SSB was low,and there were significant differences in species composition.Among the 219 species in the aboveground vegetation and SSB,61 species were found only in soil seeds,accounting for 27.85%;34 species were found only in aboveground vegetation,accounting for15.52%.The average Sorensen similarity index between aboveground vegetation and SSB was at a low level(<0.3).The main reason for the difference between the aboveground vegetation and the SSB was that the dominant species of the aboveground community and the species of trees and shrubs have a low contribution to the formation of the SSB.In addition,tree and shrub species present in aboveground vegetation were also found in SSB with less than 50%of the total.(3)The size and species composition of SSB were significantly affected by the composition and partial characteristics of aboveground vegetation.The aboveground vegetation characteristics could partially explain the changes in the species composition of the SSB(29.60%–31.44%).Herb density was the main aboveground vegetation feature that affects the density,richness and diversity of the surface(0–10cm)SSB.Compared with the surface SSB,the above-ground vegetation characteristics had less influence on the deep layer(10–20 cm).The SSB characteristics of forest communities were generally more affected by aboveground vegetation characteristics than those of shrub and meadow communities.Canopy closure was significantly negatively correlated with surface herb density and richness,and was the main vegetation feature affecting the species composition of the 0–10 cm SSB.Herb density was the main vegetation feature affecting the species composition of the 10–20 cm SSB.In addition,shrub density,shrub coverage,herb density,herb richness and coverage also affected the species composition of SSB to varying degrees.(4)Elevation and slope were the dominant environmental factors affecting the density,richness and diversity of SSB in the study area.In addition to direct effects,elevation and slope can indirectly affect the input and output of SSB by changing soil physicochemical properties.There were differences in the response of SSB to different influencing factors in the microenvironment in different seasons.The density,richness and diversity characteristics of SSB in spring(April)and summer(July)were more affected by soil physicochemical properties and topographic factors than in autumn(October),and were significantly affected by soil bulk density and water content.The SSB in autumn was more sensitive to the change of surface vegetation characteristics.In the process,the contents of SOM,TN,AK and AP generally had significant indirect positive effects on the density,richness and diversity of SSB by affecting the characteristics of surface vegetation.The germination rate had a significant direct negative effect on the characteristics of the SSB.In addition,higher soil bulk density and water content lead to the inactivation of soil seeds,thus having a significant direct negative effect on the SSB.(5)A dry storage environment could significantly maintain the activity of the SSB and alleviate the loss of soil nutrients during long-term storage.The germination rate of the SSB decreased by 9.74%–15.15%and 57.00%–58.66%after 6 months and 12months without the tarpaulin.The SSB germination rate decreased by 12.34%–14.94%and 45.67%–47.40%,respectively.Similarly,soil nutrients such as SOM,TN,AK and AP decreased by 16.88%–17.99%,12.30%–15.30%,and 10.77%–11.24%,respectively,after 12 months of storage without tarpaulin.and 21.66%–22.50%;and after taking rainproof measures for storage for 12 months,the above reduction ratios were 4.80%–6.88%,4.47%–7.83%,2.17%–4.13%and 2.02%–4.69%.(6)Both topsoil mulching and spraying could exert the ecological restoration potential of the SSB,and tiling and mulching was better in terms of restoration effect.Soil seeds began to germinate in late April,and the community density,coverage,height and diversity reached their peaks from late June to early July.The plant community restored by tiling and covering soil was higher than the plant community restored by spraying in various indicators.The change of soil physical structure caused by the addition of water-retaining agents,binders and other water-retaining soil-fixing materials might lead to a decrease in the germination rate of the SSB.In contrast,the subsoil environment under natural conditions was more conducive to the ecological restoration potential of the SSB.release.Changing the formula of the sprayed seed layer substrate to make it conform to the natural topsoil environment could be one of the ways to improve the utilization rate of SSB and reduce the waste of topsoil materials.