Water absorption is affected by the nitrogen supply to rice plants

Plant growth and photosynthetic ability have been frequently demonstrated to increase with nitrogen (N) supply. N can also promote changes in root water absorption and shoot water status via mechanisms that remain poorly understood. This study aims at investigating the effects of N supply on water absorption. A hydroponic experiment with two independent rice varieties (cv. 'Shangyou63' hybrid indica and cv. 'Yangdao6' conventional indica, China) supplied by three distinct N levels was performed in a greenhouse. Physiological characteristics were analyzed after a few weeks. Compared to low N supply (20 mg center dot L-1), exposure to high N supply (100 mg center dot L-1) increased the light-saturated photosynthetic rate (A) and water use efficiency (WUE) by 17 % and 22 %, respectively, in Shanyou63 and by 43 % and 26 %, respectively, in Yangdao6. The leaf water potential was significantly decreased in Shanyou63 but not in Yangdao6. There were increases in the rate of water uptake and the root hydraulic conductance (L (r) ) under high N supply in both rice cultivars; these changes were accompanied by increased transcription levels of aquaporins (AQPs), decreased aerenchyma formation and root porosity, and decreased root lignin content. Under high N supply, Yangdao6 also exhibited much higher AQP activity, lower aerenchyma and root porosity compared with those of Shanyou63, indicating that Yangdao6 had an increased ability to absorb water compared with that of Shanyou63. The enhanced expression of AQPs and decreased root aerenchyma and lignin contributed to increased water absorption ability under high N supply. In addition, the responses of each of the two rice cultivars (hybrid and conventional) to N supply is related to their water uptake ability, resulting from root porosity and an increase in AQP activity.