[Compensation effect of re-watering after different drought stresses on source-sink metabolism during tuber expansion period of potato.]

The compensation effect of re-watering after drought has been widely reported in various crops during different growth stages. It is considered as an important self-regulation mechanism for plants to resist abiotic stresses and also an efficient utilization of limited water resource. In this study, two rounds of re-watering after drought treatments were carried out during tuber expansion period of potato, to investigate the drought threshold of potato and explore the potential mechanisms of compensation effect with source-sink aspect. We used virus-free plantlets of "Atlantic" potato as experimental materials. Four treatments were included: sufficient water supply (W), re-watering after mild drought (D₁-W), re-watering after medium drought (D₂-W) and re-watering after severe drought (D₃-W). The results showed that potato yield exhibited an over-compensation effect after two rounds of D₁-W treatment, with water use efficiency and yield being increased by 17.5% and 6.3%, respectively, compared with the sufficient water supply. D₂-W treatment had no significant effect on potato yield, but water use efficiency was increased by 8.4%, indicating a near-equivalent compensation effect. On the contrary, D₃-W treatment did not show any compensation effect in yield. In addition, leaf chlorophyll content, net photosynthetic rate, and leaf area were all reduced after drought treatment, indicating a reduction in "source" size and activity. After re-watering, D₁-W and D₂-W treatments showed over-compensation and compensation effects through improving source supply capacity. Meanwhile, re-watering after moderate drought increased the sink activity through significantly enhancing the activities of key enzymes in tubers (sink), thus increased the average weight of tubers. In conclusion, re-watering after moderate drought stress during potato tuber expansion period had compensation and over-compensation effects on both source and sink, and thus could compensate for the drought-induced yield loss and improve water use efficiency.