Variation Characteristics Of Organic Matter Functional Groups And Microbial Communities In Channel Sediment

Sediment transport and deposition is very important to biogeochemical cycle process in terrestrial ecosystem.As the carrier of soil organic matter and microorganism,sediment particles deposited in river channel and pond dam will not only lead to reservoir deposition and river bed elevation,but also significantly affect the material transformation and carbon cycle process.Under the condition of sediment migration,the composition and distribution of organic matter and soil microorganism in sediment will be significantly affected,but the response characteristics of organic matter and microorganism to sediments migration are not clear.It is of great significance to study the spatial dynamic changes of organic matter functional groups and microbial communities caused by sediment particle migration in the gully of the watershed,which is of great significance to the biogeochemical cycle of terrestrial ecosystem under erosion landform.Based on the typical small watershed(Wangdonggou small watershed)in the gully area of Loess Plateau,five sediment sample collection points are set up along the channel from the ditch head,upstream,middle,downstream and outlet according to the length and gradient of the channel.After rainfall on August 7th,2020,sediment samples from different spatial positions are collected.The following four aspects of the channel sediment particles were studied by settlement pipeis classification,Fourier transform infrared spectroscopy and high-throughput sequencing:(1)the spatial variation characteristics of channel sediment particles.(2)The spatial variation of the functional groups of organic matter in the channel sediment.(3)The composition and spatial variation of bacterial community in sediment of channel.(4)The composition and spatial variation of Fungi Community in sediment of channel.The following main results were obtained:(1)There was significant spatial difference in the size of sediment along channel(P<0.05).The particle size of 250?m only existed in the gully head(27.9%)and upstream(11.8%);63?250?m was grade increased first and then decreased along the channel.Compared with the gully head,the upstream,middle and downstream increased 41.4%,51.8%and 16.3%,respectively;<63?m was increased gradually from the ditch head(34.9%)to the exit(64.2%);In addition,the content of organic carbon(SOC),total nitrogen(TN),and available phosphorus(Olsen-P)in sediment increased by 222.2%,146.6%and 75.5%from the ditch head to the outlet respectively;And SOC,TN and Olsen-P and he proportion of<63?m particle size was significantly positive(P<0.01),and 63?250?m particle size was negatively correlated.(2)The organic matter in the channel sediment mainly includes alcohol(C-OH 3432cm^-1,average relative content 41%),aromatic group(C=C or C=N 1437 cm^-1,30%),carboxyl group(-COO 1156 cm^-1,19%),aromatic amide(C=O 1630 cm^-1,7%)and aliphatic group(C-H 2925 cm^-1,3%);The spatial changes of official energy mass in different grain grades(P<0.05),but in the 63?250?m particle size was the most obvious,among which the aliphatic group(active functional group)decreased 48%from ditch head(2.3%)to middle reaches,then gradually increased to 2.2%of the export,while aromatic amide(inert functional group)increased(7.8%)first and then decreased(export 5.5%);The change of official energy group in<63?m fraction is relatively small.The stability of sediment organic matter(C=C/COO or C=C/C=O)in the channel is decreased first and then increased.Compared with the ditch head,the stability of the organic matter in the channel is reduced by 20.1%,23.9%,13.6%and 11.4%respectively,which may be related to 63?250?m changes,and the grain grades show<63?m,and The functional groups in<63?m were more stable along the channel(3)There are obvious spatial differences in bacterial communities in channel sediment.From the gully head to the outlet,the relative abundance of Proteobacteria decreased by 20.2%,cyanobacteria and verruco microbiota increased by 280%and 420%,respectively;The?-diversity decreased significantly along the channel(P<0.05),and the observed species index,Shannon index and Chao1 index decreased by 21.6%,8.7%and 21.2%,respectively.The relative abundance of Proteus,cyanobacteria and verruca in 63?250?m and<63?m grains varied significantly,The?-diversity decreased significantly from gully head to outlet(The?-diversity index is relatively high in<63?m fraction).In addition,the bacterial network structure gradually tends to be stable along the channel,and the modularization coefficient decreases from 0.56 at the gully head to 0.38 at the outlet.The ability of anti-interference at the outlet is the strongest.In 63?250?m and<63?m,the network structure also has the same trend along the channel.(4)There were significant differences in fungal communities from the gully head to the outlet.The relative abundance of Ascomycota decreased by 40%along the channel,basidomycota and chytrdiomycota showed a significant trend of decreasing first and then increasing,and increasing first and then decreasing,respectively(P<0.05),?-The diversity decreased gradually from gully head to outlet.The relative abundance of Ascomycota decreased by 35%and 47%,Basidiomycota increased by 125%and 82%,respectively,in 63?250 and<63 fractions,and chytera increased by 400%in the middle reaches.Fungal community in each particle size fraction The?-diversity decreased significantly along the channel(among which,the?-diversity in<63?m grain size fraction was the highest)In addition,the fungal community network structure was gradually stable along the gully,and the modularity coefficient decreased gradually from the gully head(0.59)to the outlet(0.52),but the modularity coefficient decreased first and then increased from the gully head(0.45)to the middle reaches(0.34)and then to the outlet(0.57)in the 63?250?m grains.(5)The spatial distribution of organic matter functional groups and microbial communities will be significantly affected by the migration of sediment particles in the channel.From the gully head to the outlet,the sediment organic matter functional groups,bacterial community and fungal community were greatly affected by 63?250?m fraction.At the same time,there was a significant relationship between bacterial and fungal communities and organic matter functional groups,among which Proteus,acidobacteria and Curvularia were significantly correlated with aromatic amides(C=O),Ascomycota,chytrium and Mucor were significantly correlated with carboxyl(-COO),aromatic(C=C)and aromatic amides(C=O).The migration and deposition of sediment particles in the channel will significantly affect the composition and distribution of functional groups and microbial communities.Sediment particles should be considered as an important factor in the study of ecological changes caused by erosion.Meanwhile,the relationship between organic matter functional groups and microbial communities under the condition of grain size change is more helpful to understand the biogeochemical process of terrestrial ecosystem under erosion landform.