Fig. 1
From: Suppressed N fixation and diazotrophs after four decades of fertilization
a Nitrogen fixation rates in different fertilization treatments. b Network diagram with nodes colored according to each of the three main ecological clusters (modules #1–3). c Operational taxonomic unit (OTU) number properties of the dominant diazotrophic genera in the three main ecological clusters. d Relative abundance of the ecological clusters in different fertilization treatments. Different letters indicate the values that differ significantly among treatments at P < 0.05 (Duncan’s test) in bulk soil (A, B, C) and rhizosphere soil (a, b, c). BS: bulk soil, RS: rhizosphere soil. Fertilization treatments: control, non-fertilization; NPK fertilization, NPK (urea, superphosphate, and potassium chloride); NPK + WS, NPK with wheat straw; NPK + PM, NPK with pig manure; NPK + CM, NPK with cow manure (NPK + CM)