How nitrogen fixation is modulated in response to different water availability levels and during recovery: A structural and functional study at the whole plant level

AIMS: The aims of this work were (1) to analyze concomitantly both structural and functional responses of pea plants subjected to decreasing water availability and (2) to evaluate their ability to recover after the drought period. METHODS: A pot experiment compared the growth and the nitrogen nutrition of pea plants exposed, during their vegetative stage, to seven water availability levels. RESULTS: Our results showed that the plant first reacted to water deprivation by maintaining root growth during drought and secondly to a nitrogen deficiency by allocating more carbon to the nodules responsible for nitrogen acquisition during recovery. The specific activity of nodules was negatively impacted by water stress during drought, fully recovered afterwards except after a severe water stress and the number of nodules initiated during recovery depended on the nitrogen nutritional index of the plant at the end of the drought period. This strategy allowed the plant to recover sufficiently and to maintain high values of yield components at harvest, except after a severe water stress, which reduced seed number. CONCLUSION: Our findings revealed that water availability levels did not change plant strategy in response to drought but increased the responses observed.