Changes in NO3− and K+ uptake by four species in flowing solution culture in response to increased irradiance |
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Authors: | J. H. Macduff A. Wild |
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Affiliation: | The AFRC Inst. for Grassland and Animal Production, Hurley, Maidenhead, Berks, SL6 5LR, UK.;Dept of Soil Science, The Univ. of Reading, London Road, Reading RG1 5AQ, UK. |
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Abstract: | Net rates of NO3? and K+ uptake were compared for oilseed rape (Brassica napus L. cv. Jet neuf), perennial ryegrass (Lolium perenne L. cv. S23), Italian ryegrass (Lolium multiflorum Lam. cv. Augusta) and wheat (Triticum aestivum L. cv. Fen-man) in flowing solution culture during a 4-day sequence of low-low-high-high natural irradiance. Concentrations of NO3? (10 μM) and K+ (2.5 μM) in solutions were maintained automatically and hourly variation in net uptake of these ions was measured. During the 2 days of low irradiance (<1 MJ m?2 day?1) the uptake rates of both ions by all species were low at <1 mmol NO3?, m?2 h?1 and <0.4 mmol K+ m?2 h?1. Uptake increased in each species during the first day of high irradiance (7.90 MJ m?2 day?1) to >4 mmol NO3? m?2 h?1 and >1.4 mmol K+ m?1 h?1. These higher rates were maintained throughout the following night. The lag-time between maximum irradiance and the onset of the highest acceleration in uptake was greater for NO3? (5–8 h) than for K+ (≤1 h) in rape, wheat and Italian ryegrass. Uptake of NO3?, by perennial ryegrass showed an almost constant acceleration for 18 h following maximum irradiance. In all species the measured maximum inflows (uptake rate per unit root length) of both ions were greater than theoretical maximum potential inflows to a non-competing infinite-sink root in soil, by factors of 7 and 36, respectively, for NO3? and K+, averaged over all species. |
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Keywords: | Diurnal patterns, ion uptake Brassica napus Italian ryegrass Lolium perenne Lolium multiflorum nitrate oilseed rape perennial ryegrass potassium Triticum aestivum wheat |
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