Reciprocal transfer of carbon and nitrogen by decomposer fungi at the soil-litter interface

We have investigated whether decomposer fungi translocate litter-derived C into the underlying soil while simultaneously translocating soil-derived inorganic N up into the litter layer. We also located and quantified where the translocated C is deposited within the soil aggregate structure. When C-13-labeled wheat straw was decomposed on the surface of soil amended with N-15-labeled inorganic N, we found that C and N were reciprocally transferred by fungi, with a significant quantity (121-151 mug C g(-1) whole soil) of litter-derived C being deposited into newly formed macroaggregates (> 250 mum sized aggregates). Fungal inhibition reduced fungal biomass and the bidirectional C and N flux by approximately 50%. The amount of litter-derived C found in macroaggregates was positively correlated with litter-associated fungal biomass. This fungal-mediated litter-to-soil C transfer, which to our knowledge has not been demonstrated before for saprophytic fungi, may represent an important mechanism by which litter C enters the soil and becomes stabilized as soil organic matter within the macroaggregate structure. (C) 2003 Elsevier Science Ltd. All rights reserved.