Interactive effects of nitrate and long-term waterlogging on growth, water relations, and gaseous exchange properties of maize (Zea mays L.)

The interactive effect of additional amount of NO3-N and long-term waterlogging on maize was studied in glasshouse conditions. Forty-two-day- old plants were subjected to continuous flooding for 21 days at three different NO3-N regimes (196, 294 and 392 mg N kg-1 soil). Shoot fresh mass and leaf area of waterlogged plants reduced significantly at two higher NO3 regimes. Leaf water potential was generally decreased, whereas osmotic potential increased in all waterlogged plants but much reduction in leaf water potential was found at the highest external NO3 regime. Leaf turgor potential decreased due to waterlogging but this decrease progressed with increase in external NO3 concentration. Chlorophylls 'a' and 'b' increased in non-waterlogged plants with increase in NO3 concentration of the growth medium, but these two pigments decreased significantly due to waterlogging particularly at the two higher NO3 regimes. Chlorophyll a/b ratio increased linearly in non-waterlogged plants with increase in external NO3 regimes but the ratio remained almost unchanged due to waterlogging. Waterlogging caused a reduction in net photosynthesis and stomatal conductance but no effect of additional amount of NO3 was observed on these two variables. Transpiration was also decreased as a result of waterlogging but a marked reduction in this variable was observed at the highest external NO3 concentration. Water-use efficiency increased with increase in external NO3 concentration in both waterlogged and non-waterlogged plants. Although waterlogging caused a reduction in substomatal CO2 concentration, it generally increased in both waterlogged and non-waterlogged plants due to supplementary NO3, particularly at its highest concentration. From these results, it is clear that supplementary NO3 in the growth medium of maize plants experiencing long-term waterlogging had injurious effect on growth.