Common mycorrhizal network may not facilitate plant species coexistence under very low fertility conditions

Here, we assessed if the establishment of a common mycorrhizal network (CMN) could facilitate plant species coexistence and improve plant productivity. For that we conducted a mesocosms experiment to grow serradella (Ornithopus sativus Brot., a nitrogen fixing legume) and maize (Zea mays L., a C4 grass). Besides the native arbuscular mycorrhizal inoculum, we further inoculated the mesocosms with a commercial mixture of arbuscular mycorrhizal fungal spores. The establishment of a CMN (and of plant roots) was prevented by physically disrupting a potential connection between the two plant species every week. After 12 weeks of growth in a greenhouse, we measured foliar SPAD values, harvested the plants and analyzed plant biomass and mycorrhizal traits, soil organic matter and water content. Although not always significant, disturbance increased plant biomass and density, and leaf SPAD values. Also, disturbance increased the percentage of hyphae in serradella roots and tended to increase all mycorrhizal components for both species. While there were no differences in soil organic matter concentration between treatments, there was an increase in relation to the original soil mixture. Contrary to our hypothesis, our results suggest that frequently disturbing the CMN (and plant roots) had a positive effect on plant productivity possibly by preventing plant species competition. Moreover, the increase in soil organic matter observed in all treatments highlights the crucial role that vegetation cover plays in controlling soil degradation and desertification in drylands, and in stimulating soil function and resilience.