deletions | additions       diff --git a/From_lab_to_field_Although__.md b/From_lab_to_field_Although__.md  index cdeb23d..bcfce2d 100644  --- a/From_lab_to_field_Although__.md  +++ b/From_lab_to_field_Although__.md 
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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.   As the apatite crystals are below the root scale, 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 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. 
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##Mineral incubations  Long-term soil incubation of minerals in mesh-bags is a different approach to study mineral weathering.