Soil Seed Bank Dynamics Along An Elevational Gradient In Subtropical Forests In Guangxi,South China

The soil seed bank(SSB),defined as the sum of all surviving seeds on or buried in the soil,plays an important role in determining future forest community composition and health of forests.However,it is not fully understood how abiotic factors affect the abundance and diversity of forest composition by regulating the regeneration capacity of SSB.In the present study,I used 13 permanent sample plots within the elevation range of 400?1850m in four subtropical evergreen broad-leaved forests in Guangxi,southwest China as the research objective,and measured the abiotic conditions(including elevation,canopy openness,slope,aspect,soil p H)and soil nutrients(total nitrogen [N],total carbon [C],C:N ratio,available phosphorus [P],available potassium [K],calcium [Ca],iron [Fe],magnesium [Mg],manganese [Mn],and sulfur [S])in these sample plots.In this study,eight quadrats with an area of 3m2 were set in each plot.Soil samples(a total of 2068 samples)were collected and then placed in the greenhouse for germination experiment.The germinated seeds were counted,identified and taxonomized,and the following indexes were calculated:(1)seedling abundance determined as the total number of emerged seedlings,(2)species richness calculated as the total count of morpho-species,(3)Shannon-Wiener diversity index of seedlings in SSB,(4)Simpson index,(5)Chao 2 richness estimator,(6)number of species represented by only one individual(Singletons),and(7)number of species that occur only in one plot(Uniques).The correlation between abiotic factors and soil seed pool community characteristics was determined by using structural equation modeling.The main findings are:(1)the increase in elevation and canopy openness resulted in lower abundance,species richness,diversity and fewer rare species in SSB.The influence of microsite conditions showed that(2)slope and aspect effect on SSB species abundance was greater than that of SSB diversity.Basically,the SSB abundance and richness was lower in steeper slopes but its negative effect seems to be along an indirect pathway through soil p H and nutrients such as Mn and S.(3)Soil seed abundance and soil p H are positively correlated.(4)Soil phosphorus was significantly correlated with the indicators of soil seed bank characteristics,the lower the soil phosphorus content,the lower the species richness,diversity and rarity.Through the study of soil seed banks in the large elevation gradient range of subtropical forests in Guangxi,this study reveals the correlation between abiotic factors and soil seed bank community characteristics,and provides basic data and scientific basis for further research on the effects of soil seed banks on forest regeneration and restoration and for evaluating the regeneration potential and forest health status of the subtropical forests of Guangxi.