Waterlogging tolerance in the forage legume Melilotus siculus

Messina (Melilotus siculus, Fabaceae) is a waterlogging-tolerant annual forage legume, but data were lacking for the effects of waterlogging on nodulated plants reliant on N₂ fixation. Konnerup et al. find that plants inoculated with the appropriate rhizobia, Ensifer (syn. Sinorhizobium) medicae, formed nodules.

Nodulated plants grew similarly well as plants fed NO₃^–, both in drained and waterlogged conditions. In waterlogged conditions the relatively high respiration rates of nodules relied on O₂ movement via the secondary aerenchyma (phellem) in hypocotyl, roots and the outer tissue layers of nodules, which we demonstrated using microelectrodes.