add dead root experiment assay and protocol

assays/DeadRootExperiment/protocols/DeadRootExperimentProtocol.md

+## Dead root experiment
+
+Mature root systems from Gifu and Col-0 plants grown in potting soil in the greenhouse were harvested from flowering plants (13-week old *Lotus*, 7-week old *Arabidopsis*), washed several times in water, padded on kitchen paper to remove moisture and dried in big glass petri dishes at 120 °C for 1 h. Note that Gifu plants had a few small, most probably ineffective root nodules. Pieces of the dried, dead roots were planted into FlowPots under sterile conditions, and SynCom (*LjAt*-SC3) inoculation was performed as described above. Dead roots were recovered from the FlowPots after 5, 12 and 19 d of incubation, and washed and stored as described above for live roots.
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