Spatial And Temporal Distribution Pattern Of Planktonic Microbial Eukaryotes In Ganjiang River Basin

Microbial eukaryotes are highly diverse,wide-distributed,and various in sizes and shapes.Although tremendous advances in the distribution research of microbial eukaryotes have been achieved,variation of temporal distribution and the deviation from the use of universal primers are commonly ignored.In fresh water drainage of different ecological environment,the main stream and tributaries interpermeating tributary import will impact the abundance and diversity of biological community in the fresh water drainage.However,the research on the spatial and temporal distribution pattern of microplanktonic eukaryotes in an entire watershed is still insufficient.On another hand,the controversy about the two distribution patterns of micro-planktonic eukaryotes,that is restricted distribution or widespread distribution is still unsettled.Recently,a systematic study on the community of planktonic microbial eukaryotes of Ganjiang River basin for one year was conducted at those issues via the method of high-throughput sequencing using specific primer for the high variant region of the V4-rRNA gene of the small ribosome subunit of the eukaryotic microplankton.The results are shown as following.(1)The planktonic microbial eukaryotes in Ganjiang River basin were highly diverse and rich.In the study,a total of 4330788 effective sequences were obtained,and they were identified as 4903 Operational Taxonomic Units(OTUs)and 1206 species.It covered all the supergroups of the eukaryotic system with determined developmental position,and only a small percentage of species have high abundance.Archaeplastida and Hacrobia were the most widespread group.Cryptomonas curvata was the dominant species with abundance taking up 9.47% of the total abundance,and it was detected in all the sampling points.(2)Unknown species were detected in all the sample points,accounting for 13.6% of the total OTUs and they were even detected in the most widely distributed groups.For example,the unknown species OTU4250 was the second most abundant species and it is detected in all sample points.It was unveiled that although Stramenopile MAST-2,MAST-12 and MAST-6 were commonly classified as typical Marine groups,they were detected in Ganjiang River,validating that they are not unique Marine groups.(3)The results of the study supported the restricted distribution hypothesis of environmental selection.According to the fitting of the distribution frequency of OTUs,the distribution frequency of OTUs at the sample points conformed to the equation: y=466.6-143.8(1-exp(-x/859.3-444.5(1-exp(-x/8.995)),R2 = 0.9721.(4)There was no correlation between the seasonal variation of species abundance and the seasonal variation of species richness.The seasons order of species richness was: winter > spring > autumn > summer,and the seasons order of species richness was: spring > summer > autumn > winter.In winter,Cryptomonas curvata(OTU1250)was the dominant species in the Ganjiang River basin,as its abundance is more than 3 times of that of any other species.The number of seasonally unique OTUs accounted for 14.2% of the total number of OTUs,and the eukaryote community variated seasonally in all samples,indicating that seasonal sampling surveys were necessary.(5)The rank of abundance of functional group in any season was as follows: autotrophs > free-living heterotrophs > parasites,and the difference in abundance of functional groups was of one or two orders of magnitude.Parasites were more abundant in winter than in other seasons.(6)The confluence was one of the important reasons that resulted in the changes of the microplanktonic eukaryotic community in the main stream.The number of OTUs unique in the upper stream of the main stream accounts for 29% of the total number of OTUs,but it gradually decreased from the upper stream to the lower stream,and the OTUs of the main stream and that of the tributary became gradually consistent.(7)Temperature,and difference of time and location are important factors for the variation of microplanktonic eukaryotic community.