Microeukaryotic Diversity In Relation To Environmental Variables In Saline-alkali Soil And Marine Sediment

Microbial eukaryotes including protists, algae, fungi and meiofauna areubiquitous in soil and marine sediment and probably play key roles in maintainingecosystem function. Moreover, microeukaryotic diversity and their geographicdistribution have controversially debated in recent years. The study on themicroeukaryotic diversity is limited by the availability of appropriate method, and thusthe knowledge on the diversity and distribution of microbial eukaryotes as well as theirrelationships with environments is far from being fully discovered, especially in someextreme microhabitats.Here, we utilized the improved Ludox-Quantitative Protargol Stain (Ludox-QPS)method which was originally developed for marine sediment to assess ciliate diversityin soil. The method was tested with three soil samples and compared with a ciliate-specific Denaturing Gradient Gel Electrophoresis (DGGE) and direct count method.The Ludox-QPS method obtained significantly higher number of ciliates with highertaxonomic resolution than the direct count, and revealed higher diversity than theDGGE as well as subsequent gene sequencing. Besides, we developed a new indirectDNA extraction method for investigating the molecular diversity of soil microbialeukaryotes which combined the silica sol Ludox density centrifugation and thetraditional Sodium Dodecyl Sulfate (SDS)-based DNA extraction method. Its efficiencywas evaluated and compared with the direct lysis methods (the SDS-based method and commercial DNA extraction kit). The indirect method could obtain a high purity ofintracellular DNA and had high efficiency in estimation of molecular diversity of soilmicrobial eukaryotes.We investigated the ciliate diversity and their relationships with theenvironments in the different type of saline-alkali soil using both the moleculartechniques and morphological methods. The species richness and abundance of activeciliate were decreased with increasing the salt content, and even no active ciliates wereobserved from soil when the salinity was close to5‰by the Ludox-QPS method. Incontrast, the results based on the ciliate-specific DGGE indicated that if the soil salinitywas under30‰, high diversity of ciliates could be maintained in spite of salinityincrease. Moreover, the similarity in saline soil ciliate genetic diversity generallyexhibited a decreasing trend as distance increased and soil salinity might be the mostsignificant factor affecting the distribution of ciliates. Colpodea, Spirotrichea,Litostomatea and Oligohymenophorea were commonly found in different type of saline-alkali soil. The ciliate community in saline-alkali soil was similar at class level, while itwas significant different at species level. The coastal soil near the sea hosted a ciliatecommunity of both marine and soil taxa.We investigate the response of microeukaryotic and prokaryotic moleculardiversity to the change of environment in particular salinization in coastal soil of theLaizhou Bay and Yellow River Delta, China by the DGGE as well as sequencing. Theobvious shifts of DGGE patterns were detected along an environmental gradient amongsites, while statistically indistinguishable among seasons. Soil salinity and pH as well asorganic matters might be the main factor affecting the distribution of microeukaryotesand prokaryotes in the coastal soil.An increasing trend of the microeukaryotic diversity was detected from north tosouth in the sediments of the Yellow Sea. Water depth, Chl a and the abundance of Copepod might be the most significant factor regulating the distribution of microbialeukaryotes. Moreover, a higher diversity was found in the sediments of the ChangjiangRiver estuary than that in the Yellow Sea. Location rather than seasonal change wasimportant in regulating the community composition of microeukaryotes in sediments.Water depth and TOC might be the main factor affecting the distribution of soilmicroeukaryotes in the Changjiang River estuary. The results based on the clone libraryrevealed that the summer samples of each sites were with higher diversity than that ofspring samples. The protozoan diversity decreased from spring to summer, while thediversity of meiofauna increased. Bacillariophyta was only detected in spring anddisappeared in summer, while Dinoflagellata were present in both seasons. Thedominant group of fungi was changed between different seasons. High diversity andabundance of ciliates existed in the sediments, and the planktonic Choreotrichia andOligotrichia could encyst and reserve in the sediments as environmental deterioration.In sum, our study indicated that the distribution of most microbial eukaryotes wasgeographically restricted, while some species adapted to the special environment couldexist in different locations with similar environmental conditions. Soil salinity might bethe main factors regulating the distribution of microeukaryotes in the saline soil, andwater depth, Chl a and organic matter were important restricting factors in marinesediments. The diversity of microbial eukaryotes was higher in the marine sedimentsthan that in the coastal saline-alkali soil, and the lowest in the inland saline-alkali soil.The data indicate that both molecular and microscopy-based methods have particularshortcomings, and it was difficult to identify all species by a single method. Thus,combined approaches will provide more information than either alone.