Steel-tray nutrient-diffusing subst

Steel-tray nutrient-diffusing substrate sampler. Top: sampler without the lid attached
showing the internal frame of the sampler. The four agar-filled jars at the rear show stages
in securing the filter-paper colonisation surfaces to the jars. The phosphorus-enriched
agar jars are dark in colour. Bottom: nutrient-diffusing substrate sampler after incubation
with the lid attached (the upstream end is marked with red paint on the left). Treatments
from the far side are: control, nitrate + phosphate, phosphate, nitrate .