Diurnal regulation of rice N uptake ability under interrupted N supply.

Plants take up nitrogen (N) both day and night. The diurnal variation in N uptake results from interactions between aboveground and belowground tissues. We examined the long-term effects of interrupted N supply (day only or night only) under hydroponic conditions to test whether plant acclimatisation response to the interrupted N supply differs by day or night. Seedlings experienced 32 days under daytime-fed (DF), night-time-fed (NF), or continuous (CT) N supply. The root N uptake rate (NUR) differed between DF and NF from day 3 of treatment, after which NUR was significantly increased (by up to 82%) in DF and NF plants. The increased NUR during each half-day did not fully compensate for lost access to N during the other half-day, resulting in lower N accumulation by the end of the treatment. The reduction was smaller in DF plants than NF plants. The underlying mechanism of diurnal variation of N uptake is discussed in terms of transpiration demand and gene expression in roots.