mark smits edited From_lab_to_field_Although__.md  about 8 years ago

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# From lab to field  Although numerous experiments clearly show that (mycorrhizal) fungi do have an impact on mineral dissolution (see previous section), the significance of fungal mycorrhizal  weathering on soil and global scale weathering rates remains controversial. This ongoing controversy is caused by both the challenge to quantify the fungal mycorrhizal  contribution in the field, and a series of persisting misconceptions. Modelling is a useful tool to test the scope of fungal mycorrhizal  weathering concepts. In this section we will review the available field data and modelling modeling  work on mycorrhizal weathering, and discuss the most persistent misconceptions in this research field.   Without doubt does vegetation have a substantial positive effect on soil mineral weathering .   It remains the question though, how much influence the associated rhizosphere-microorganisms 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.  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}.   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  hyphae colonizing apatite grains.  In an influential paper Blum *et al.* \cite{Blum_2002} used this technique to compare the plant-Ca source of different tree species with contrasting mycorrhizal associations.  As