deletions | additions       diff --git a/From_lab_to_field_Although__.md b/From_lab_to_field_Although__.md  index 5378a55..06cc47d 100644  --- a/From_lab_to_field_Although__.md  +++ b/From_lab_to_field_Although__.md 
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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.  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}. 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.  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.  Apatite is a calcium-phosphate mineral, and as P has no stable isotopes, the uptake dynamics can only be studied via the Ca ion (or potentially the ¹⁸O/¹⁶O in the phosphate group .  As apatite is generally only a minor mineral in the soil mineral matrix, its contribution to the soil solution Ca pool is minor compared to other minerals.  If the Ca isotopes in the plant is more similar to the signature in apatite than in the soil solution, it indicates that the plant takes up Ca directly from the apatite crystal. Which is As the apatite crystals are  below the root scale, indicating it indicates  a selective uptake via mycorrhizal hyphae colonizing apatite grains. In an influential paper Blum *et al.* \cite{Blum_2002} applied this technique, but as in their study area, the different mineral sources did have similar Ca isotope ratios, they used the ratio between Ca and Sr instead.  Using element ratio ratios, instead of isotope ratios,  increases the risk of fractionation. Already in 1926 Fay warned for the use of Ca/Sr ratio to trace sources of Ca \cite{fay_strontium_1926}. Most of the Ca taken up by trees comes from litter recycling. In a comparable northeastern mixed forest, the annual Ca import from weathering in the rooting zone is less than 0.3% of the annual Ca uptake , which was a 4 times smaller flux than the annual atmospheric deposition \cite{Dijkstra_2002}.  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.   minerals in mesh-bags is a different approach to study mineral weathering.   rates  Turpault et al. 2009: strong increase in weathering rate labradorite in presence roots, in top 10 cm, apatite only at 2.5cm. No distinction between root effect and mycorrhizal effect (local acidification?).  -->