A quantitative revision of the waterlogging tolerance of perennial forage grasses

Waterlogging tolerance of eight C-4 and seven C-3 perennial forage grasses was reviewed. The median waterlogging duration was similar between species' type, ranging between 18 and 21 days. Inter- and intra-species variability was found in shoot and root biomass in response to waterlogging. Urochloa brizantha (C-4), Brachiaria hybrid (C-4) and Dac tylis glomerata (C-3) were the less tolerant species to waterlogging (shoot biomass median of 45%, 53% and 80% of controls), while U. humidicola (C-4), Paspalum dilatatum (C-4), Festuca arundinacea (C-3) and Lolium perenne (C-3) were the most tolerant (shoot biomass median of 97%, 101%, 87% and 94% of controls). A similar ranking of responses was found among species for root biomass. The formation of aerenchyma/root porosity (a key trait for waterlogging tolerance) was evaluated mainly in U. humidicola and P. dilatatum (C-4 waterlogging-tolerant species), which showed considerable constitutive porosity (13% and 32%) and final values of 30% and 41% under waterlogging. Net photosynthesis and stomata) conductance as typical leaf physiological responses matched species' waterlogging tolerance, with the impact of hypoxia higher in C-3 than in C-4 species. Gaps in knowledge about waterlogging tolerance in forage grasses are: (i) additional studies on C-3 perennial grasses for temperate pasture areas prone to waterlogging, (ii) identification of traits and responses aiding plant recovery after waterlogging (and also during the stress), (iii) reassessment of waterlogging tolerance considering plant developmental stage (e.g. adult vs young plants), and (iv) evaluation of sequential (i.e. waterlogging - drought) and combined (i.e. waterlogging + salinity) stresses, which often co-occur in pasture lands.