Growth resilience is an important aspect of plant adaptability to drought. Nitrogen (N) application is a common cultivation measure, but its impact on growth resilience after rewatering of alfalfa (Medicago sativa) is still unclear. In this study, alfalfa grown under different N supplies (3 mmol·L-1 and 7 mmol·L-1) was rewatered after drought, which was simulated by adding polyethylene glycol-6000 in the nutrient solution. The growth, nitrogen content, content of non-structural carbohydrates, and activity of enzymes for sucrose conversion were monitored at the end of drought, and on days 7 and 24 after rewatering. On day 24 after rewatering, the dry matter of plants grown under high N condition increased by 11.0％, showing "compensatory growth", whereas the plants grown under low N condition did not recover and their dry biomass was 19.6％ lower than that of the control group (without drought treatment). Because of the "drought memory", the plants grown under high N conditions significantly increased root-to-shoot ratio, root starch, root soluble sugar, and nitrogen content, whereas the root-to-shoot ratio, root sugar, and nitrogen content in roots did not change in plants grown under low N condition at days 7 and 24 after rewatering. On day 7 after rewatering, the activity of sucrose phosphate synthase (SPS) in leaves significantly decreased (P < 0.05) in plants, whereas the activity of sucrose synthase (SS) and acid convertase (AI) significantly increased (P < 0.05). On day 24 after rewatering, plants grown under high N conditions consistently maintained higher SS activity (P < 0.05). The results indicate that nitrogen application increased the SS activity of plants; increased the accumulation of dry matter, starch, and soluble sugar in the root; and facilitated the growth resilience of alfalfa after rewatering.
drought resistanceresilienceN supplyroot shoot ratiosoluble carbohydratestarchenzymes involved in sucrose metabolism
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