Eukaryotes in soil aggregates across conservation managements: Major roles of protists, fungi and taxa linkages in soil structuring and C stock

The stabilization of soil organic carbon (SOC) promoted by conservation agriculture (CA) depends on soil aggregation. Aggregation protects SOC and creates heterogeneous microhabitats hosting diverse soil biota which in turn promote aggregation. A long-term experiment, studying the interaction of tillage with nitrogen (N) fertilization on a soybean-wheat rotation, was used to investigate eukaryotic community diversity, composition, and structure within small macroaggregates (sM) and occluded microaggregates (mM). Using high-throughput Illumina sequencing, we found (i) a different eukaryote diversity response to management intensification across soil aggregates and soil depths; (ii) a conserved core community composition of eukaryotes across CA treatments and aggregates at surface and subsurface layers; (iii) a different effect of tillage on eukaryotic community structure in sM and mM along the soil profile according to N availability; (iv) a positive association of protists, and fungi with the amount of sM and mM, and their SOC content; (v) a stronger complexity of within- and cross-domain networks (eukaryotes and eukaryotes-prokaryotes) in mM than in sM at surface layer. Overall, our findings demonstrate for the first time that protists together with fungi play major roles in soil structuring and C cycling, and that Cercozoa represent hubs in soil biota aggregate networks.