The effects of different external nitrate concentrations on growth of <i>Phaseolus vulgaris</i> cv. Seafarer at chilling temperatures

Summary The effects of different applied nitrate concentrations (1 to 50 mol m 3 ) on growth of Phaseolus vulgaris cv. Seafarer at temperatures around 15°C was examined. Total plant dry weight and carbon content decreased sharply with increased applied nitrate 1 to 10 mol m ‐3 then decreased slightly with further increases in applied N. Total plant reduced ‐N content increased sharply with increased applied nitrate concentration from 1 to 5 mol m ‐3 , changed little with increased applied nitrate from 5 to 25 mol m ‐3 , then increased when applied nitrate was increased from 25 to 50 mol m ‐3 . Nitrate concentration in all tissues increased sharply with applied nitrate increased from 1 to 10 mol m 3 and showed a further increase at 50 mol m 3 applied nitrate. Fresh weight to dry weight ratio for all leaves and specific leaf area for all secondary leaves increased sharply with applied nitrate concentration from 1 to 5 mol m ‐3 then decreased with applied nitrate 25 to 50 mol m 3 Secondary leaf chlorophyll concentration decreased sharply when applied nitrate increased from 1 to 5 mol m ‐3 but increased with applied nitrate from 25 to 50 mol m ‐3 . Initially, the rate of leaf extension was greater at 20 mol m ‐3 applied nitrate than 1 mol m ‐3 applied nitrate. It is proposed that decreased growth with increased applied nitrate in the range 1 to 10 mol m ‐3 is due to increased leaf damage caused by a greater rate of leaf expansion.