“Ecological Filtering” Function Of Dicranopteris Synusisa On Degraded Slope In South China

Dicranopteris(Gleicheniaceae),a typical pioneer,dominant and keystone species in degraded slop of South China,distributes in southern of the Yangtze River in China,Japan,Vietnam and India.Dicranopteris is an indicator plants of acid soil.It is light-demanding,acid-resisting,drought and barren tolerant,and easy to shapes as a single dominant species layer community in wasteland.Dicranopteris could effectively stabilize the soil,promote soil nutrient accumulation,increase microbial diversity and accelerate soil material circulation,which possessing a positive effect on the management of red soil erosion area and soil erosion area.Besides,Dicranopteris synusia restricts the growth of most species in species regeneration and allows a few species to establish,which could be seen as“ecological filtering”.Seedlings which break through the Dicranopteris synusia are constructive species in the late successional stage and play a crucial role for the direction and path of later successional stage.The research on the"ecological filter"function of Dicranopteris synusia could provide some technical reference for the structure and function of single stand optimization or secondary forest,and for guide some ecological restoration measures(species selection,human intervention)that could be taken to reasonably promoting the community succession in South China.However,it has not been involved in previous studies.In this study,seeding retention experiment,seedling regeneration experiment and microenvironment experiment were conducted to explore how the Dicranopteris synusia work as an"ecological filter"and its mechanism.The main results are as follows:(1)In the experiment on seed retention effect,the seeds collected from the seed bank were all common pioneer species in degraded slope of South China,with a total of 14 species.The species with the largest number of seeds were Trema tomentosa,Rhodomyrtus tomentosa,Melastoma candidum,Baeckea frutescens and Mussaenda Pubescens.The seed were mainly herbaceous and shrub species,and lack of tree species.The seed bank density,the number of individuals,richness,Shannon Wiener index(H)and Simpson index(d)in the root blanket layer of Dicranopteris were higher than those in the red soil layer and the open plot.For example,the seed bank density in the root blanket layer of all plots was more than 40 ind/m~2,while the seed bank density in the red soil layer and the blank plot were 5-24 ind/m~2 and 6.67ind/m~2,respectively.The number of species in the root blanket layer was 2-5,while that in the red soil layer and blank ground was merely 1 or 0.(2)In the experiment of seedling settlement,the Dicranopteris synusia had a screening effect on seedling survival.The root blanket layer of Dicranopteris played a decisive role in seedling survival rate,and most species could not survive under the layer of Dicranopteris.Among the 12 species,R.tomentosa,I.asprella and M.candidum seedlings had relatively high survival rates under the synusia,which all belongs to shrub species.The highest survival rate of the three species was 26.7%in the treatment of root blanket layer preservation,while the survival rate of other seedlings were lower,which are likely to become"filter species"or"screening species"to break through the limitation of Dicranopteris synusia.(3)In the study of microenvironment effect of Dicranopteris layer,compared with the microclimate effect of bare ground,Dicranopteris layer significantly buffered high temperature(the maximum average temperature buffered 0.8℃),kept warm and moisture(the daily difference of soil temperature was about 0.5-1℃,and the air humidity was close to100%),resisted strong light(photosynthetically active radiation could be reduced to zero)and reduced wind speed(the wind speed was basically below 2 m/s,and even reduced to zero).The SOM of the root blanket layer of the Dicranopteris sample plot could reach more than three times of the red soil layer and the bare ground.The HN content was twice than the red soil layer,and the maximum AP value could reach 1.2mg/kg,which was significantly higher than that in the bare ground.The maximum AK content in the root blanket layer could reach20mg/kg,and the total exchangeable base in soil(Na,Ca,Mg,CEC)was larger than that in bare ground.In this study,combined with the microenvironment experiment,seed retention experiment and seedling settlement experiment of Dicranopteris synusia,it could be considered that Dicranopteris synusia has the function of"ecological filtering".The dense structure and root blanket layer of Dicranopteris synusia inhibit the settlement of most species by intercepting seeds and"screening"seedlings of different species.However,most shrub species still could survive under the synusia of Dicranopteris,and the root blanket layer of Dicranopteris played a decisive role in the filtering process.