| Taihe Wei Township is located in Leiyang City of Hengyang City,situated in the central Hunan Province,China.The climate is characterized by a typical subtropical monsoon humid climate,and the soils are mainly composed of a large area of purple soil.The purple soil has a series of ecological characteristics,such as low organic matter content,below-average mineral nutrient content,weak soil anti-erodibility and wash durability,sparse vegetation,serious soil erosion,and shallow soil layer.Even there will be ecological problems,for instance,exposed bedrock,adverse ecological environment,and extremely difficult vegetation restoration.In this paper,three adjacent natural plant communities(grassland community,shrub community,and deciduous broad-leaved forest community),with basically similar environmental conditions(site,soil and climate),were selected to represent a succession sequence in the typical purple soil slope by using the method of space-for-time substitution.The fixed sample plots in different succession stages were set up.The community surveys were investigated by the quadrat sampling method,and community biomass was measured by the harvest method and calculated by the established biomass estimation model.The aim of this study was to investigate the changes of species composition,diversity and spatial structure of natural plant community and the spatial distribution pattern of biomass in different succession stages,and to analyze the relationships between community biomass and species diversity or soil physicochemical properties,further revealing the changing mechanisms of composition and structure and biomass of plant communities with community succession in purple soil hilly region of central Hunan Province,and providing evidence for predicting thesuccession trend of plant communities,vegetation restoration and reconstruction,and the utilization and protection of natural vegetation resources.The main results were summarized as follows:(1)There were 33,36 and 48 species of grassland community,shrub community and deciduous broad-leaved forest community,belonging to 31,34 and 40 genera and 19,21 and 28 families,respectively.With the succession of vegetation,woody plants increased by 37 species and herbaceous plants decreased by 22 species.In three plant communities along vegetation succession,the individual numbers of woody plants were 5700,28800,and 87514,and that of herbaceous plants were 190950,31575,and 31800,respectively.The similarity of grassland community and shrub community or deciduous broad-leaved forest community decreased gradually,were 0.464 and 0.074,respectively.These results indicated that during vegetation succession,the plant composition of community tended to be complicated,species species increased,the quality of plant increased,the difference of species composition increased,dominant species changed significantly,and the species richness of different levels of the communities was obvious.(2)During vegetation succession the community structure tended to be complex,and there were differences in the species diversity among herb layer,shrub layer and tree layer.In herb layer,Margalef index,Shannon-Weiner index,Simpon index and Pielou index increased first and then decreased with vegetation succession.In shrub layer,Margalef index increased,Shannon-Weiner index and Simpon index increased and then decreased,and Pielou index decreased with vegetation succession.The a diversity index of tree layer was higher than that of shrub layer and herb layer.(3)With the increase of DBH,the individual numbersof woody plants in grassland community,shrub community and deciduous broad-leaved forest community showed a downward trend,the family numbers first increased and then decreased,and the species numbers had relatively large changes.With the increase of height level,the individual numbers of woody plants in grassland community,shrub community and deciduous broad-leaved forest community showed a downward trend,the family numbers first increased and then decreased,and species numbers had relatively large changes.(4)The total biomass of grassland community,shrub community and deciduous broad-leaved forest community were 4.926,9.741,and 151.456 t/ha,respectively.The aboveground biomass of these three plant communities were 1.833,5.737,132.703t/ha,respectively,and the underground biomass were 2.881,4.004,18.753 t/ha,respectively.The aboveground biomass,underground biomass and total biomass all increased with vegetation succession.The percentage of underground biomass in total biomass decreased with vegetation succession,from 58.49%to 14.13%.The biomass distribution patterns of herb layer and shrub layer were different in different succession stages.The underground biomass of herb layer and shrub layer in grassland community were higher than the aboveground biomass,while in shrub community and deciduous broad-leaved community,the aboveground biomass of herb layer and shrub layer were higher than the underground biomass.The aboveground biomass of tree layer in deciduous broad-leaved forest community was higher than underground biomass,and the biomass of different components was as follows:stems>roots>branches>leaves.The vertical spatial distribution patterns of biomass were as follows:the biomass of herb layer was higher than shrub layer in grassland community,while the biomass of shrub layer was higher than herb layer in shrub community,and the order of biomass in deciduous broad-leaved forest community was:tree layer>shrub layer>herb layer>litter layer.(5)In herb layer and shrub layer,there were significant positive correlations between the aboveground biomass and the Shannon-Weiner index of,but there were no significant correlations between the total biomassand the Shannon-Weiner index,and the blowground biomass and the Shannon-Weiner index.The positive correlation between community biomass and soil AK,AN,pH value,water content gradually increased with vegetation succession.In grassland community,the total biomass and soil physicochemical properties,except for SOC and soil moisture content,were negatively correlated,the aboveground biomass had the significant negative correlations with soil moisture content and SOC,and the underground biomass was significantly negatively correlated with soil TN and AP.In shrub community,the total biomass was significant positively correlated with soil AK,AN and pH,but was significant negatively correlated with soil bulk density,TK and TP.The aboveground biomass had the significant positive correlations between soil water content,Ca and pH,while had the significant negative correlations with soil AP,SOC,Mg,TP and TK.There were significant positive correlations between underground biomass with soil AK,TN,AN and pH,and the significant negative correlations with soil bulk density,TK and TP.In deciduous broad-leaved forest community,the total biomass and underground biomass had significant positive correlations with soil AK,AN,soil bulk density,soil moisture content and pH,while the total biomass,aboveground biomass and underground biomass had significant negative correlations with soil TN,Ca and SOC. |
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