DOI: 10.5061/dryad.np5hqc016
title: Protists regulate microbially-mediated organic carbon turnover in soil aggregates

description: Soil protists, the major predator of bacteria and fungi, shape the
 taxonomic and functional structure of soil microbiome via trophic
 regulation. However, how trophic interactions between protists and their
 prey influence microbially mediated soil organic carbon turnover remains
 largely unknown. Here, we investigated the protistan communities and
 microbial trophic interactions across different aggregates-size fractions
 in agricultural soil with long-term fertilization regimes. Our results
 showed that aggregate sizes significantly influenced the protistan
 community and microbial hierarchical interactions. Bacterivores were the
 predominant protistan functional group and were more abundant in
 macroaggregates and silt + clay than in microaggregates, while omnivores
 showed an opposite distribution pattern. Furthermore, partial least square
 path modeling revealed positive impacts of omnivores on the
 C-decomposition genes and soil organic matter (SOM) contents, while
 bacterivores displayed negative impacts. Microbial trophic interactions
 were intensive in macroaggregates and silt + clay but were restricted in
 microaggregates, as indicated by the intensity of protistan-bacterial
 associations and network complexity and connectivity. Cercozoan taxa were
 consistently identified as the keystone species in SOM degradation-related
 ecological clusters in macroaggregates and silt + clay, indicating the
 critical roles of protists in SOM degradation by regulating bacterial and
 fungal taxa. Chemical fertilization had a positive effect on soil C
 sequestration through suppressing SOM degradation-related ecological
 clusters in macroaggregate and silt + clay. Conversely, the associations
 between the trophic interactions and SOM contents were decoupled in
 microaggregates, suggesting limited microbial contributions to SOM
 turnovers. Our study demonstrates the importance of protists-driven
 trophic interactions on soil C cycling in agricultural ecosystems.
description: #### Sample information **Id** **Sample_ID** **Aggregate**: LA,
 macroaggregates (250-2000 μm); MA, microaggregates (53-25 μm); SA, silt +
 clay (&lt; 53 μm). **Fertilization type**: Control, non-fertilization;
 NPK, chemical fertilization; M, organic manure; MNPK, a combination of
 chemical and organic fertilization. #### Abiotic factors * The abiotic
 factors of of different soil aggregates were determined. **TC**: total
 carbon (g/kg); **TN**:total nitrogen (g/kg); **C/N**: the ratio of soil
 total carbon to total nitrogen; **SOM**: soil organic matter (g/kg);
 **AN**: ammonium-nitrogen (mg/kg); **TP**: total phosphor (g/kg); **AP**:
 available phosphorus (mg/kg); **pH**: soil pH. #### Protistan functional
 groups * The protistan ASVs were assigned into functional groups based on
 their feeding modes. Then, the relative abundances of the protistan
 functional groups in soil aggregates were caculated, including:
 **Bacterivore, Eukaryvore, Omnivore, Parasites, Phototrophs,
 Plantpathogens, Saprotrophs**, and **uncertain**. #### Protistan groups
 (at class level) * The relative abundances of the majority of protistan
 classes in soil aggregates were analysed by high-throughput sequencing
 (protistan 18S rRNA gene V4 region), including: **Filosa-Sarcomonadea,
 Variosea, Filosa-Thecofilosea, Oomycota, Colpodea, Tubulinea,
 Spirotrichea, Chrysophyceae, Filosa-Imbricate,** and **the other
 classes**. #### C-decomposition genes * The signal intensities of
 C-cycling functional genes involveded in organic C decompositions in soil
 aggregates were examined by GeoChip 5.0 (60K), including: **Starch,
 Inulin, Hemicellulose, Pectin, Cellulose, Cutin, Chitin, Vanillin** and
 **Lignin**. #### Bacterial groups (at phylum level) * The relative
 abundances of the majority of bacterial phylum/class in soil aggregates
 were analysed by high-throughput sequencing (bacterial 16S rRNA gene V4
 region), including: **Actinobacteria, Alphaproteobacteria,
 Gemmatimonadetes, Acidobacteria, Betaproteobacteria, Chloroflexi,
 Gammaproteobacteria, Deltaproteobacteria, Verrucomicrobia, Bacteroidetes,
 Planctomycetes, Nitrospirae,** and **the others**. #### Fungal groups (at
 class level) * The relative abundances of the majority of fungal class in
 soil aggregates were analysed by high-throughput sequencing (fungal ITS 1
 gene), including: **Sordariomycetes, Zygomycota_Incertae_sedis,
 Dothideomycetes, Leotiomycetes, Tremellomycetes, Ascomycota_unidentified,
 and** the **others**.