Effect of temperature on growth and nitrogen mineralization of fungi and fungal-feeding nematodes

Dish and column microcosms containing alfalfa-sand medium were established to determine effect of temperature on growth and N mineralization ability o f two fungi (Rhizoctonia solani and Botrytis cinerea) and two nematodes (Ap helenchus avenae and Aphelenchoides composticola). The microcosms were incu bated at 15, 20, 25 and 29 degreesC for 21 days. In the dish microcosms, hy phal growth rates of both fungal species increased with temperature in the range of 15-25 degreesC. Above that temperature range, the growth rate of R . solani remained almost constant while that of B. cinerea decrease conside rably. The population growth rate of A. avenae increased with temperature b etween 15 and 29 degreesC on colonies of R. solani and B. cinerea in dish m icrocosms. The growth rate of A. composticola also increased in the range o f 15-25 degreesC but decreased greatly beyond that temperature range indepe ndent of the fungal species as food source. Inorganic N (NH4+ + NO3-) was c ollected from each column microcosm by leaching every 3 days. In the column s containing R. solani, there was a significant effect of temperature on th e amount of N detected in the fungus+A avenae or A. composticola but not in the fungus alone columns. The total amount of N was greatest at 29 degrees C for A. avenae and at 20 degreesC for A. composticola columns, concurrent with the population growth rates of the nematodes. In the columns containin g B. cinerea, the effect of temperature on the amount of inorganic N was no t significant in either the fungus alone or fungus+nematode columns, althou gh the population growth rates of the both nematode species were highest at 20 degreesC. For B. cinerea, the N amount across temperatures was the same or larger for the fungus alone as for the fungus+nematode columns. In gene ral, the contribution of fungal-feeding nematodes to N mineralization was s mall in any combinations of fungus and nematode species at any temperature. Similarity in C/N ratio of the fungal and nematode biomass, organic substr ate C/N ratios too low for measurable increase in net mineralization by the nematodes and small reproduction of the nematodes in the column microcosms were probable contributory factors.