Responses Of Soil Protists To Different Fertilization Treatments

Protists include all eukaryotes except plants,fungi and animals.They are an essential component of the soil microbiome.Protists play important roles in soils by regulating organic matter decomposition,catalysing biogeochemical nutrient cycling processes and maintaining soil fertility and plant productivity.They play a key role in the microbial food web as consumers of bacteria,fungi and other small eukaryotes.The concept of protists as important indicators of soil health has not received enough attention in terms of long-term localized fertilization.Most of the previous studies focused on the main microorganisms in soil(e.g.,bacteria and fungi),but relatively few studies have been conducted on protists.To further improve our understanding of protists,we used amplicon sequencing to explore the mechanisms by which soil protists respond to different fertilization treatments.Based on the Dongyang Experimental Base in Shanxi Province,soil without fertilizer(CON),phosphorus and potassium(PK),nitrogen and potassium(NK),nitrogen and phosphorus(NP),and nitrogen,phosphorus and potassium(NPK)were selected in this study.Phyllosphere,root endosphere,rhizosphere soil and bulk soil samples were collected in September 2019.Soil samples analysed for basic physical and chemical properties,and DNA was extracted from all samples,followed by amplicon sequencing.In order to explore the response mechanism of soil protists to different fertilization treatments,the changes in soil physical and chemical properties,soil bacterial community and soil fungal community were analyzed comprehensively.Our main results are as follows:(1)Protists were dominated by the supergroups Rhizaria,Stramenopiles,Alveolata,Amoebozoa and Archaeplastida across the four sorghum compartments.There were significant differences in protistan community compostions and diversity among different sorghum compartments.The diversity and richness of phyllosphere and root endosphere protists were significantly lower than those of rhizosphere and bulk soils.The composition of phyllosphere and root endosphere protists was significantly different from that of rhizosphere and bulk soils.(2)Specific protistan consumers and parasites are responsive to inorganic fertilization.In each of the four sorghum compartments,specific parasitic or consumer protists were sensitive to fertilization.(3)Spearman correlation analysis showed that there were significant correlations between protists and bacteria and fungi and there was a significant positive correlation between protists,bacteria and fungi.Protists can regulate soil microbial community by preying on some bacteria and fungi,and bacteria and fungi can resist predation by protists via releasing specific antibiotics and secretions,thus regulating the composition of protist community.Biological factors were the main influencing factors of protistan community in the other three sorghum compartments except phyllosphere.(4)There were significant differences in bacterial and fungal community diversity,richness and composition among different sorghum compartments.There was a rapid loss of microbial diversity from soil-root-leaves.(5)In the same sorghum compartment,the addition of inorganic fertilizer had no significant effect on the bacterial and fungal community diversity,but some specific bacterial and fungal genera were more sensitive to fertilization,resulting in changes in microbial community structure.Different fertilization treatments had no significant effect on the composition and diversity of protistan community.Compared with the control,the addition of inorganic fertilizers(PK,NK,NP,NPK)in the same habitat had no significant effect on the alpha diversity and community structure of protists.Taken together,this study investigates effects of different fertilization regimes on soil protists,extends our understanding of soil protists in agroecosystems and reveals the effects of biotic and abiotic factors on the change of protistan community Considering their dynamic responses to agricultural management practices and intensive interactions with bacterial and fungal taxa,future studies should disentangle the principles how protists regulate the taxonomic composition and functions of soil microbiomes,which will open up a new avenue to promote plant performance and sustainable agriculture through manipulation of the protistan communities.