A quantitative review of soybean responses to waterlogging: agronomical, morpho-physiological and anatomical traits of tolerance

The impact of waterlogging on crops has increased during the last decades due to climate change, being considered the second most important abiotic stress after drought in soybean, with yield reductions of up to 80%. In this review, we performed a quantitative review from 54 papers about waterlogging effects in soybean. Yield losses are greater (57%) with waterlogging occurring at reproductive stages between R1 and R3 compared to vegetative stages, which is mostly related to a diminished number of pods per plant. Waterlogging impacts on biological nitrogen fixation, with losses of about 30 and 50% in nodule number and weight, with the greatest reductions in reproductive stages. The nitrogenase activity is drastically reduced with water excess but can quickly restore after. Losses in photosynthesis are about 30–50%, mostly related to reduced stomatal conductance and poor N status. Soybean can also develop aerenchymatous tissue in roots, hypocotyls and nodules, which may alleviate the anoxia generated by waterlogging by facilitating oxygen transport. Further efforts should be invested in investigating the effect of waterlogging on nodulation and the impact and subsequent recovery of root growth.