Growth and nitrogen mineralization of selected fungi and fungal-feeding nematodes on sand amended with organic matter

Isolates of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Pen icillium sp., Rhizoctonia solani, Stemphylium sp., Thielaviopsis basicola, and Verticillium dahliae were cultured on potato-dextrose agar (PDA), barle y-sand and alfalfa-sand substrates in petri-dish or in column microcosms. N -mineralization by fungi and fungal-feeding nematodes in combination or fun gi alone was assessed. Numbers of Aphelenchus avenae or Aphelenchoides comp osticola supported by the fungi were measured every 7 days. Times for full colonization of the substrates by fungi ranged from 5 to 15 days. Rhizocton ia solani and B. cinerea on PDA supported the largest A. avenae and A. comp osticola populations, respectively. Penicillium sp. was a nonhost for A. co mposticola and A. avenae. Rhizoctonia solani, B. cinerea, V. dahliae, and F . oxysporum supported significantly more nematodes than the other four fung al species. The ranked order of fungi based on the amount of N mineralized in columns free of nematodes was A. alternata (with a rate of 0.052 mu g N/ g-sand per day), Stemphylium sp., V. dahliae, T. basicola, B. cinerea, F. o xysporum, R. solani, and Penicillium sp. (with a rate of 0.0045 mu g N/g-sa nd per day). The presence of A. avenae resulted in significant increases in mineral N, compared to nematode-free columns colonized by F. oxysporum, R. solani, and T. basicola alone. The presence of A. composticola resulted in significant increases in mineral N, compared to nematode-free columns colo nized by A. alternata, B. cinerea, F. oxysporum, and R. solani alone. There was more mineral N in columns in the presence of A. composticola than A. a venae in most cases.