deletions | additions       diff --git a/From_lab_to_field_Although__.md b/From_lab_to_field_Although__.md  index 06cc47d..bf7da8f 100644  --- a/From_lab_to_field_Although__.md  +++ b/From_lab_to_field_Although__.md 
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It remains the question though, how much influence the associated mycorrhizal fungi have on this vegetation effect.  Due to the slow kinetics of soil mineral weathering, and the complex soil matrix, a direct estimation of the contribution of mycorrhizal fungi on the weathering process is challenging.  Three different approaches have been adopted to address the impact of mycorrhizal weathering: 1) historical weathering markers, 2) stable isotopes to trace the source of tree nutrients and 3) quantifying incubated minerals in contrasting soils.  In addition, modeling can be a powerfull tool to upscale proposed mycorrhizal weathering mechanisms to soil or even global scale weathering processes.  ##Historical weathering markers  Tunnels, as described in \cite{Jongmans_1997} are the only quantifiable fungal markers of weathering that remain visible over geological time.  Unfortunately, fungal tunneling either reflects only a small portion of the total effect of fungi on the weathering process, or the fungal impact is negligible, as tunneling contributes less than 0.5% tot total mineral weathering \cite{Smits_2005}.  In a recent paper Koele et al. \cite{Koele_2014} showed that mineral tunneling is not exlusively found under ectomycorrhizal vegetation, but also in forest soils, never exposed to ectomycorrhizal vegetation.  ##Isotope tracing  Stable isotopes of especially Ca and Sr have been used extensively to source the origin of Ca in drainage water .   Applied to plant tissues, it could potentially traceback plant nutrients back to their primary source.   It has been primarily used to study the apatite weathering. 
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A closer look at the data presented in \cite{Blum_2002} clearly separates ectomycorrhizal trees with a high Ca/Cr ratio (the two coniferous species) and trees with a low Ca/Sr ratio in their leaves (the two deciduous species). Although in principle this difference could be explained by host specific mycorrhizal communities, with the both coniferous species hosting mycorrhizal fungi with stronger capability to weathering apatite, a more obvious explanation is that Ca/Sr fractionation is different during throughfall and litter recycling. One hint in that direction can be find in the Blum et al. data itself: throughfall Ca/Sr ratios are lower than the leave data in the coniferous species, indicating fractionation within the tree needles, while throughfall and leave Ca/Sr ratios are similar in the deciduous species.  Up to now, isotope techniques have not provided convincing evidence of a major mycorrhizal contribution in mineral weathering.  ##Mineral incubations  Long-term soil incubation of minerals in mesh-bags is a different approach to study mineral weathering.