Nutrient absorption by pea plants during dinitrogen fixation. 2. Effects of ambient acidity and temperature.

Abstract

Nutrient uptake and biological dinitrogen fixation were studied using effectively nodulated pea plants which had been grown hydroponically for 6 wk in nutrient sol. of pH 4.0, 5.5 or 7.0. The pH of the root medium was kept constant by automatic titration and the temp. maintained at 13 deg C throughout. Although the N content of the plants grown at pH 4.0 and 7.0 was lower in comparison with that of plants of the pH 5.5 treatment, no N deficiency symptoms were observed. About the same number of nodules was formed in each of the treatments but they were smallest in the pH 5.5 treatment. Nevertheless, the total amount of dinitrogen fixed/plant at pH 5.5 was larger than that at higher or lower acidity. This was due to a higher nitrogenase activity/unit of nodule wt., which could be ascertained by an in vivo acetylene reduction test. In all cases more nutritive cations than anions were absorbed resulting in net proton extrusion by the roots. Both cation and anion uptake and hence the extent of proton release were affected substantially by ambient acidity. Plants grown at pH 7.0 generated 2.3 times as much acidity as plants grown at pH 4.0. The symbiotic dinitrogen fixing process was repressed by raising the temp. to 25 deg which resulted in no DM production and proton release and accelerated the onset of maturation. (Abstract retrieved from CAB Abstracts by CABI’s permission)