Fig. 2

A–E LEfSe results revealed protist biomarkers (from supergroup level to family level) that were sensitive to nitrogen fertilizers (no nitrogen addition (control) or nitrogen addition (N) or nitrogen + straw addition (NS)) in the black soil in summer (a) and autumn (c), in the fluvo-aquic soil in autumn (d) and in the red soil in summer (b) and autumn (e). There are five circular rings in the cladogram, each circular ring deposit all taxa within a taxonomic level; the circular ring from inside to outside represents supergroup, phylum, class, order, and family, respectively. The node on the circular ring represents a taxon affiliating within the taxonomic level. Taxa that had significantly higher relative abundance in a certain treatment within each soil type were color-coded within the cladogram according to the Protist Ribosomal Reference (PR2) taxonomy. Soil samplings were conducted in summer and autumn after 2-year fertilizers application. _X represents unidentified lower taxonomic ranks within the respective category