Effects of nitrogen and glucose on saprophytic survival of Ophiobolus graminis in buried straw

SUMMARY Calcium nitrate prolonged the saprophytic survival of Ophiobolus graminis (Sacc.) Sacc. in artificially colonized straws buried in soil in the laboratory, whether supplied to the soil (at 12·5 or 100 mg nitrogen/100 g soil) or to the straws before colonization (at 0·5 or 1·0 g nitrogen/100 g straw). Glucose (at 2·5 g/100 g soil, and at 10 g/100 g straw) shortened survival. When straws colonized in the presence of 0·5 g nitrogen/100 g straw were buried in soil supplied with 14·1 mg nitrogen/100 g soil, the level of soluble soil nitrogen reached equilibrium at 2–4mg/100g soil; this allowed rapid straw decomposition and, although the added soil nitrogen prolonged survival in straws that remained undecomposed, it also accelerated substrate exhaustion. Addition of 100 mg nitrogen/100 g soil was supra‐optimal for survival: although some nitrogen was necessary for maximum survival, the equilibrium concentration of soluble nitrogen (24–56 mg/100 g soil) was high enough in this case to have an inhibitory effect in addition.