Soil Seed Bank And Vegetation Restoration Study On The Loess Plateau

The research aimed to explore the potential role of soil seed bank in the process of plantcommunity construction, the vegetation restoration and reconstruction in the degradedecosystems. Moreover, this study provided a theoretical basis and scientific foundation forrestoration and reconstruction of degraded ecosystems. Study was carried out in three zonalvegetations on the Loess Plateau including typical grasslands, forest grasslands and desertgrasslands. The methods of a combined operation of historical data collection with fieldinvestigation and laboratory analysis were used to systematically study the characteristics ofsoil seed bank, and its relationship with vegetation in three zonal vegetations. The mainresults were concluded as follows:1. The basic characteristics of soil seed bank on the Loess Plateau were clarified, suchas species composition, species diversity, density and spatial distribution pattern. Soil seedbank was dominated by Poaceae, Compositae species, and herbaceous plants. Soil seed bankdensity ranged as1388~9853seeds·m-2in typical grasslands,567~1210seeds·m-2in forestgrasslands and31~482seeds·m-2in desert grasslands, indicated that restoration of degradedecosystems on the Loess Plateau was not seed limited. Species richness and diversity of thesoil seed bank had the same position in three grassland types, and ranked as follows: typicalgrasslands> forest grasslands> desert grasslands. Most viable seeds were scattered at the≤10cm depth of the soil. Soil seed bank had obvious vertical distribution pattern that seeddensity significantly reduced with the depth increasing (except seed density in the litter layer),except that seed density at the0~5cm depth and at the5~10cm depth were similar in desertgrasslands.2. The relationship between soil seed bank and vegetation, and the potential contributionof soil seed bank to the process of plant community construction, and the vegetationrestoration and reconstruction in the degraded ecosystems were revealed. The similarity indexbetween soil seed bank and vegetation was very low on the Loess Plateau, Jaccard similarityindex ranged as0.29~0.38in typical grasslands,0.15~0.21in forest grasslands,0.05~0.27indesert grasslands. In typical grasslands, soil seed bank played a minimal role in the process ofvegetation succession under the grazing exclusion, and could not accurately predict thedirection of vegetation succession and development. In forest grasslands, although soil seed bank played an important role in maintaining the species diversity, it was not an importantmeans for forest natural regeneration. The seedlings had extremely low survival rate and weregreatly sparse, the natural population regeneration depended mainly on sprouting instead ofsoil seed bank. In desert grasslands, it was likely that the potential of shrub layers restorationdepending on soil seed bank was very low. Overall, the establishment of the vegetation inthese communities is more likely to rely on seed dispersal and asexual recruitment, and thepotential role of degraded ecosystems restoration depending on soil seed bank was very lowon the Loess Plateau.3. Impacts of disturbance (grazing and grazing exclusion) on soil seed bankcharacteristics in typical grasslands were studied. The results showed that grazing and grazingexclusion measures did not significantly change the dominant species composition of the soilseed bank, however, grazing measures made the companion species disappear from the soilseed bank and grazing exclusion protected these species to remain in the soil. Moderategrazing significantly increased the species numbers of soil seed bank, but significantreduction in long-term grazing exclusion grasslands. Species diversity of soil seed bank wassignificantly improved by short-term grazing exclusion, but was significantly reduced bylong-term grazing exclusion. Grazing and grazing exclusion significantly affected the densityof soil seed bank by changing the density at0~5cm depth, short-term grazing exclusion didnot significantly increase the density of soil seed bank, but significant increase was found inlong-term grazing exclusion grasslands. Litter biomass and thickness significantly affected theseed density, not the species number, which was the internal driver for the effects of grazingand grazing exclusion on soil seed bank. Coefficient of variation (CV) of seed bank densityfor grazing grasslands was largest, and slightly was reduced in short-term grazing exclusiongrasslands, and significantly reduced in long-term grazing exclusion grasslands. Grazing andgrazing exclusion did not significantly affect the similarity between soil seed bank andvegetation.4. The effects of succession on vegetation and soil seed bank were analyzed. During thecourse of succession under grazing exclusion measures, the vegetation showed a clearsuccession trend, however, this trend is not reflected in soil seed bank. The response of soilseed bank to disturbance is latter than vegetation. Soil seed density increased,and thesimilarity of species composition decreased with succession age increasing. The soil seedbank played an important role in the vegetation restoration in the early succession stage, andseed bank′role became weaker and weaker with succession.5. Seed quality and fate after dispersal of dominant trees were analyzed. Seed lossoccurred mainly because of vermiculating, predation and removal by animals (30%), and mildewing (15%), among which predation and removal by animals was the most importantfactor that caused seed bank depletion. Germinating or sound seeds accounted for55%,which provided enough seed source for population natural regeneration, however, theseedlings had only0.1%survival rate.6. Impacts of the geographic location (Longitude, Latitude, altitude) on thecharacteristics of the persistent seed bank in desert grasslands were revealed. In desertgrasslands, persistent seed bank density was significantly and negatively correlated withlatitude, but no significant correlation with longitude. Longitude and Latitude did notsignificantly affect the species richness and diversity of the persistent soil seed bank, and thesimilarity between the persistent soil seed bank and vegetation. Altitude did not significantlyaffect the density of the persistent seed bank, however, it significantly affected the speciesrichness and diversity of the persistent soil seed bank, and the similarity between thepersistent soil seed bank and vegetation. Species richness and diversity of the persistent seedbank, and its similarity with vegetation decreased with the altitude increasing.7. Seed persistence in the soil for145species belonging to Loess Plateau were tested,and whether and how seed mass and shape are related to seed persistence in soil were studied.Among145species with a range of growth forms, from a wide range of families, in the LoessPlateau, the species with persistent seed bank accounted for48%, and the species withtransient seed bank accounted for44%. Seed mass and shape were found to be significantlyand negatively correlated to persistence in the soil. The value of seed mass and shape as goodpredictors of persistence in the soil could be applied to the Loess Plateau. Although manyfactors affect the relationship between seed mass, shape and persistence, ease of burialappears to be the main potential interpretation.