Soil fungi appear to have a retarding rather than a stimulating role on soil apatite weathering

Abstract

Aims Vegetation stimulates, in general, soil mineral weathering. It has been hypothesized that plant-associated microorganisms, especially ectomycorrhizal fungi play a major role in this process. We studied apatite dissolution in a vegetation gradient in southern Norway to test the role of ectomycorrhizal vegetation on mineral weathering. Methods A natural occurring lead contamination, probably present since the last glaciation, caused a gradient from bare soil, via sparse grass to healthy spruce forest. We measured apatite content, soil solution chemistry, delta C-13, delta N-15, C, N and ergosterol content in soil profiles along the gradient. Results The apatite loss for each soil depth could be described by the same proton-based, dissolution function over the whole vegetation gradient. The deviation fromthe 30-40 cm depth pH model showed, in the top 20 cm, a negative correlation with ergosterol, and a positive correlation with delta C-13. These correlations could reflect an inhibiting effect of biotic activity through the production of large weight organic acids and degradation of low molecular weight organic acids. Conclusions Vegetation accelerates apatite dissolution by acidifying the soil solution, but soil fungi appeared to have a retarding, rather than an enhancing effect on this process.