Inhibition of N2fixation by white clover (Trifolium repensL.) at low concentrations of NOinf3sup−in flowing solution culture

✍ Scribed by J. H. Macduff; S. C. Jarvis; I. A. Davidson

• Book ID: 104613933
• Publisher: Springer
• Year: 1996
• Tongue: English
• Weight: 774 KB
• Volume: 180
• Category: Article
• ISSN: 0032-079X
• DOI: 10.1007/bf00015312

✦ Synopsis

The impact of sustained low external concentrations of NO; (0,10,100 and 1000 mmol m -3) on plant growth and the relative acquisition of N through N2 fixation and NO 3 uptake by established, nodulated white clover (Trifolium repens L. cv. Blanca) was studied over 28 days in flowing solution culture. Nitrogen fixation was measured by N difference and lSN dilution methods. Plants supplied with NO~-achieved higher relative growth rates (~ = 0.091 d -1) compared with 'control' plants dependent on N2 fixation (0.073 d-l). Nitrate plants showed progressive increases in shoot : root d.w. ratios from 4 to 6.5-7.6 between days 0--28, compared with 5.1 on day 28 for control plants. Increases in both nodule d.w. and numbers per plant were inhibited after day seven at all concentrations of NO 3. The severity of inhibition of N2 fixation increased with increasing NO 3 concentration and with time. The total amounts of N2 fixed per plant between days 0-7 after supplying 10,100 and 1000 mmol m -3 NO 3, respectively, were 37-39, 28-30 and 0-13%, of the total N acquired. Between days 7-28 the proportional contributions of N2 fixation to total N acquisition declined to 3, 0. 5 and 0%, respectively, in these treatments. The corresponding mean specific rates of N2 fixation between days 0-7 were, respectively, 5.4, 3.2, and 2.0 mmol N d-l g-l nodule d.w., compared with 7.9 mmol N d -1 g-i nodule d.w. for zero NO 3 plants. There was no evidence of a transitory increase in N2 fixation following the addition of NO 3, even at the lowest supply concentration.