Relationships between growth and photosynthetic charachteristics in pearl millet (Pennisetum glaucum) under limited water deficit conditions with enhanced nitrogen supplies

Effect of supra-optimal levels of N on growth, water relations and photosynthetic capacity in pearl millet under severe water deficit conditions was assessed in a pot experiment under glasshouse conditions and some parallels between growth and physiological attributes were drawn. Thirty four-days-old plants of two lines, ICMV-94133 and WCA-78 were subjected for 30 days to 224, 336, and 448 mg N per kg soil and two water regimes (100 percent field capacity and 30 percent field capacity). Increasing soil N supply proved to be detrimental under water deficit conditions on the growth of two lines of pearl millet. Watering regimes had a significant effect on net CO2 assimilation rate (Pn) and stomatal conductance of both pearl millet lines, but in contrast, there was no significant effect of varying soil N levels on these two variables. Transpiration rate (E) was significantly affected due to watering regimes and external N levels. Neither watering regimes nor N levels had significant effect on water use efficiency (WUE) of both lines of pearl millet. Watering regimes had significant effect on both chlorophyll a and chlorophyll b contents of both lines of pearl millet. In contrast, neither watering treatments nor soil N levels had significant effect on chlorophyll a/b ratios, although a slight increase in chlorophyll a/b ratio was observed under water deficit conditions. A slight increase in chlorophyll a was observed under water deficit conditions, whereas the reverse was true for chlorophyll b. Leaf turgor potential in both lines increased with increase in soil N level under water limiting conditions. Soluble sugars, soluble proteins, and total free amino acids in the leaves of both lines of pearl millet increased significantly due to water limiting treatment. From these results it is possible to conclude that supra-optimal levels of N were detrimental to the growth of pearl millet under severe water deficit conditions. In addition, the growth of pearl millet under drought stress and high N regimes was strongly associated with net CO2 assimilation rate (Pn), net assimilation rate (NAR) and relative growth rate (RGR). Considerable osmotic adjustment occurred in pearl millet plants experiencing water deficit and high N regimes.