The root nitrogen uptake response to partial nitrogen stress is related to previous nutritional status

We investigated the dynamics and factors influencing the N uptake capacity in two sub-root systems of maize seedlings under partial N stress. Maize seedlings were grown in split-root containers containing nutrient solutions. Two N application conditions prior to partial N stress (full-strength N (4.0 mM): CP; N stress: SP) were considered. Thus, two experiments were conducted: (A) four treatments: CPNc, CPN2, CPN1 and CPN0, in which half of the root system was exposed to 4.0 mM, 2 mM, 1 mM and 0 mM N (CPNc–c, CPN2–2, CPN1–1 and CPN0–0), respectively, and the other half received full-strength N (CPNc–c, CPN2–c, CPN1–c and CPN0–c); (B) four treatments: SPNc, SPN2, SPN1 and SPN0, in which both sub-root systems received 4.0 mM, 2 mM, 1 mM and 0 mM N for 6 days, respectively, after which half of the root system was maintained at original N level (SPNc–c, SPN2–2, SPN1–1 and SPN0–0) and the other half received full-strength N (SPNc–c, SPN2–c, SPN1–c and SPN0–c). At 0.25 days after treatment (DAT), CPN2–c and CPN1–c enhanced N inflow rates (Iroot), whereas CPN0–c decreased it by 27.3% compared with CPNc–c, Iroot in CPN2–c, CPN1–c and CPN0–c was uniformly enhanced at 1 DAT, but were only enhanced in CPN0–c at 5 DAT compared with CPNc–c. In contrast, SPN1–c had a significantly increased Iroot by 10.52% compared with SPNc–c, although other treatments showed a negative effect on Iroot at 0.25 DAT. At 1 and 5 DAT, Iroot in SPN2–c, SPN2–2, SPN1–c, SPN1–1 and SPN0–c were significantly lower than that in SPNc–c. Furthermore, CP significantly enhanced Iroot in non-stressed sub-roots compared with SP. Additionally, CPN2 improved shoot dry mass and N use efficiency even under SPN2. Thus, N uptake capacity in each sub-root zone varied not only depending on the severity and duration of the N stress, but was also related to the N status prior to partial N stress. Moreover, the occurrence and disappearance of the root compensatory effect were delayed with increasing N stress severity. A higher compensatory effect developed following CP, even under CPN0.