Sporulation of arbuscular mycorrhizal fungi in organic-rich patches following host excision

Soil organic matter is known to directly influence nutrient capture and affect the growth of arbuscular mycorrhizal fungi (AMF). The effect of organic-rich patches in soil on subsequent sporulation and the persistence of spores will have important implications for sustainable agricultural practices particularly as AMF spores are likely to play a significant role in soil carbon dynamics and ecosystem productivity. We have used a mesh-exclusion approach to quantify the temporal dynamics of AMF sporulation in organic-rich patches following host shoot excision. Wheat plants were grown in pots, filled with sterile sand inoculated with Glomus intraradices, Glomus mosseae or a non-mycorrhizal control. Each pot contained three 25cm3 mesh bags (35μm), filled with either farmyard manure (FYM), soil or sand. At 6 weeks post-emergence the host shoot was excised and AMF spores were quantified in each of the mesh bags and again at 24, 52, 66 and 80 days after host excision. Spore numbers were far higher in FYM than in patches of soil, although by 24 days after shoot excision the number of spores had dramatically decreased in patches of both FYM and soil; however this was followed by a significant increase in spore numbers of G. intraradices in the FYM patches. Extractable P, NO3 − and NH4 + in the mesh bags were all significantly higher in the FYM patches than in the patches of soil, although there were no differences between the control and the mycorrhizal treatments. However, the concentration of soluble phenolics in the FYM colonised by both of the AMF species significantly decreased between 0 and 24 days after host excision compared to the control. This finding provides novel insights into the nature of asymbiotic sporulation in organic-rich patches and has important implications for sustainable agricultural practices, including FYM application enhancing the ‘mycorrhizal potential’ of soil following a harvest, by increasing the amount of early colonisation in the next crop.