PLANT FOLIAR PHOSPHORUS AND SILICON CONTENT CHANGES IN RESPONSE TO ROOT FUNGAL COMMUNITIES AND SILICON ENRICHMENT

Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that supply limiting nutrients, largely phosphorus (P), to plants in exchange for carbon. Silicon (Si) is an important defence element for plants and several reports have observed a relationship between AMF colonisation and Si uptake. It is unknown how diverse soil microbial communities affect foliar Si and P concentrations, and whether improvements in foliar Si concentrations due to AMF colonisation are observed in field conditions. This is the first study to document the dual effects of AMF and Si application in a non-crop species (Brachypodium sylvaticum) and the effect of different microbial communities, on plant uptake and deposition of Si and P.
An initial glasshouse experiment used a single species AMF inoculum in combination with a Si enrichment treatment to investigate the effect on foliar Si and P concentration. The results showed that AMF improved the uptake of Si and P compared to non-colonised plants, but that different mechanisms for uptake are likely. Introducing microbial communities isolated from agricultural and woodland environments as inocula in a controlled environment showed that microbial diversity alters the efficacy of Si and P supply, and that improvements in the supply of these were not directly related to AMF colonisation. Finally, B. sylvaticum plants from woodland were sampled across two years. The results of this sampling did not show any benefit of AMF on Si and P uptake, but did reveal significant differences in P concentration over time irrespective of fungal colonisation.
Comparisons between studies using high throughput sequencing demonstrates that the methods commonly used in mycorrhizal studies may be overlooking important interactions with un-recorded organisms in the soil and roots of experimental plants. Ecologically relevant studies incorporating long-term repeated sampling are required to fully understand how microbial communities can improve Si and P nutrition in plants.