Collecting fungal mycelium using in-growth mesh bags: Effects of the sand particle size and seasonality

In-growth mesh bag technique is widely used for assessing production and turnover of the fungal mycelium in soil, but remains poorly standardized. This research aims at testing the use of quartz sand of different particle size, as a filling for in-growth mesh bags, in order to obtain a maximum amount of fungal mycelium. Mesh bags were incubated in a Norway spruce forest in Central Russia in June and September. Mycelial biomass was higher in sand of coarse (> 0.5 mm) particle size and reached maximum (up to 798 mu g of mycelium dry weight g(-1) sand) in June. A relatively short incubation time (up to 30 days) was sufficient for estimating mycelium biomass and for collecting mycelium for isotopic analyses. The delta C-13 and delta N-15 values of fungal mycelium collected at the depths of 10 and 25 cm did not differ. Mycelium was depleted by 2.5% in N-15 compared to mycorrhizal and by 3.0% in C-13 compared to saprotrophic fruit bodies. This observation should be taken into account in the isotope-based reconstructions of belowground food webs.