Diurnal patterns of nitrate assimilation in Kentucky bluegrass

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Kentucky bluegrass (Poa pratensis L.) is a major C3-type forage and turfgrass, but it is less efficient than many grasses in utilizing nitrogen(N). To determine how this grass can accommodate its greater N need, diurnal patterns of nitrate reductase activity (NRA) and nitrite reductase activity (NiRA) in its leaves and roots were examined and compared with those in barley (Hordeum vulgare L.). Plants were grown under greenhouse or growth room conditions and assayed for NRA and NiRA by optimized in vivo methods. The diurnal patterns of NRA and NiRA indicated that Kentucky bluegrass could assimilate nitrate during the night at rates greater than or similar to those during the day. Leaf NRA of Kentucky bluegrass was minimal approximately 4 and 10 h after illumination commenced and increased at night. The diurnal pattern of leaf NRA among Kentucky bluegrass cultivars did not differ significantly. In roots, NRA of Kentucky bluegrass was high in the morning and decreased sharply during the afternoon and evening, but increased again late at night. Unlike Kentucky bluegrass, barley exhibited greater leaf NRA during the day than during the night and exhibited the greatest activity 6 or 10 h after illumination commenced. In both species, the equilibrium leaf nitrate pool was 20 to 30 times larger than the ammonium pool and 3,000 to 13,000 times larger than the nitrite pool. Leaf nitrate pool size showed a diurnal pattern complementary to that of leaf NRA. Our results suggest that a nighttime N use strategy might exist in Kentucky bluegrass.

Publication Title, e.g., Journal

Journal of Plant Nutrition