A. bisporus food web reconstruction and nematode analysis by stable isotope probing
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The white button mushroom (A. bisporus) is one of the most important commercial mushroom cultivars worldwide, whose compost contains plentiful microbiota. However, little is known about the impact of nematodes on A. bisporus’ growth and the carbon flow in the compost. To investigate this, a 13C-glucose tracer study was performed, followed by counts of nematode densities which concluded with the build-up of a mathematical model of the carbon flow of this environment. First known application of LA-IRMS on nematodes for stable isotope analysis was performed, the results of which were coupled with results of PLFA biomarker studies, in order to build an interactive food web model for carbon flow tracing. Nematode population densities were shown to be too low to cause disease in A. bisporus primordia. Cultures without A. bisporus showed a lower overall number of nematodes than those with A. bisporus. Natural abundance δ13CVPDB measurements of nematodes agreed with literature values for soil nematodes and glucose tracer experiments suggested that nematodes uptake the tracer label indirectly through bacteria and fungi as second-level consumers. The model showed a drop in the bacterial and fungal biomass over the course of the experiment, with a simultaneous increase in A. bisporus biomass. Consistently with literature, simple sugars increased, and complex carbohydrates decreased over time, with increased emitted CO2. These findings highlight that nematodes in commercial A. bisporus mushroom beds do not present danger to the mycelium, with A. bisporus acting as a direct competitor to nematode populations, which consume bacteria and fungi and in doing so, support carbon flow as top-level consumers.