Influence of ammonium on the formation of mineral-associated organic carbon by an ectomycorrhizal fungus.

In this study, we examined how changes in nitrogen (N) availability affected the formation of mineral-associated carbon (C) from these two pathways. DOM was extracted from forest soils. The processing of this DOM by the ectomycorrhizal fungus Paxillus involutus was examined in laboratory-scale studies under different levels of ammonium. At low levels of ammonium (i.e. during N limited conditions), the DOM components were slightly oxidized and fungal C metabolites with iron reducing activity were secreted. Ammonium amendments decreased the amount of C metabolites and no additional oxidation of the organic matter was detected. In contrast, the hydrolytic activity and the secretion of N containing compounds increased, particularly when adding high levels of ammonium. During these conditions, N did not limit fungal growth, rather C. Though the overall production of mineral associated organic C was not affected by ammonium concentrations, the observed shifts in the activities of the ex vivo and in vivo pathways affected the composition of organic matter adsorbed onto the mineral particles. Such changes will affect the properties of the organic matter-mineral associations and thus ultimately the stabilization of SOM.IMPORTANCE Nitrogen (N) availability plays a critical role in the cycling and storage of soil organic matter (SOM). However, large uncertainties remain in predicting the net effect of N addition on soil organic carbon (C) storage due to the complex interactions between ...
Source: Applied and Environmental Microbiology - Category: Microbiology Authors: Tags: Appl Environ Microbiol Source Type: research