Nitrogen Cycle

digraph n {
  layout=circo;
  graph [bgcolor=transparent];
  node [shape=box, style="rounded,filled", fontname=Inter, fontsize=10];

  N2 [label="Atmospheric N₂", fillcolor="#fef3c7"];
  NH4 [label="Ammonium NH₄⁺", fillcolor="#dbeafe"];
  NO2 [label="Nitrite NO₂⁻", fillcolor="#dbeafe"];
  NO3 [label="Nitrate NO₃⁻", fillcolor="#dbeafe"];
  Bio [label="Plants / animals", fillcolor="#dcfce7"];

  N2  -> NH4 [label="fixation\n(rhizobia, lightning)"];
  NH4 -> NO2 [label="nitrification (Nitrosomonas)"];
  NO2 -> NO3 [label="nitrification (Nitrobacter)"];
  NO3 -> Bio [label="assimilation"];
  Bio -> NH4 [label="decomposition\n(ammonification)"];
  NO3 -> N2  [label="denitrification\n(Pseudomonas)"];
}