Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

Water stress is a primary limitation on plant growth. In previous studies, it has been found that ammonium enhances the tolerance of rice plants to water stress, but how water is related to nitrogen form and water stress remains unknown. To study the effects of nitrogen form (NH (4) (+) , NO (3) (-) , and a mixture of NH (4) (+) and NO (3) (-) ) on the growth and water absorption of rice (Oryza sativa L.) seedlings, a hydroponic experiment with water stress, simulated by the addition of polyethylene glycol (PEG, 10% w/v, MW 6000), was conducted in a greenhouse. The results showed that, compared with non-water stress, under water stress, the fresh weight of rice seedlings increased by 14% with NH (4) (+) nutrition, whereas it had decreased by about 20% with either NO (3) (-) or mixed nitrogen nutrition. No significant difference was found in the transpiration rate of excised shoots or in xylem exudation of excised roots in NH (4) (+) supply between the two water situations, whereas xylem flow decreased by 57% and 24% under water stress in NO (3) (-) and mixed nutrition, and root hydraulic conductivity decreased by 29% and 54% in plants in NH (4) (+) and NO (3) (-) nutrition conditions, respectively. Although water absorption ability decreased in both NH (4) (+) and NO (3) (-) nutrition, aquaporin activity was higher in NH (4) (+) than in NO (3) (-) nutrition, regardless of water stress. We conclude that NH (4) (+) nutrition can improve water handling in rice seedlings and subsequently enhance their resistance to drought.