The effect of soil moisture tension and nitrogen supply on nitrate reduction and accumulation in wheat seedlings

Summary The effect of soil moisture tension on nitrate reductase and on nitrate accumulation in wheat plants was studied. Nitrate reductase activity was inhibited when soil moisture tension was increased to about 3.0 bars associated with a drop in leaf relative water content to about 90 per cent. The decrease in nitrate reductase activity did not result in nitrate accumulation in short-term experiments (10 days) when plants were exposed to only 1–2 cycles of elevated soil moisture tensions. However, when the period of different moisture regimes was extended up to the flag-leaf stage, nitrate accumulated in stressed plants.Significant increase in plant nitrate concentration as a result of increased moisture tensions was only found at the high levels of added nitrogen. On the other hand, moisture tensions had no effect on the content of total nitrogen in wheat shoots, implying that nitrate reduction was rather limiting under stress conditions.An effect of soil moisture tension and nitrogen nutrition on dry matter production by wheat seedlings was also found in the long-term experiment. At the highest dose of soil nitrogen an increase in maximal soil moisture tension from 0.1 to 0.33 bars reduced plant growth; at intermediate nitrogen doses only tension higher than 2 bars reduced growth. Under complete nitrogen deficiency, plant dry matter production was very low and was not affected by soil moisture tensions.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1972 Series, No. 2185-E.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1972 Series, No. 2185-E.