Root respiration and bacterial population of roots I. Effect of nitrogen source, potassium nutrition and aeration of roots

Abstract

Abstract Spring wheat was grown in nutrient solution culture to investigate the influence of aeration, different sources of nitrogen and discontinuation of potassium supply on root respiration and on the number of root bacteria. By definition root respiration included oxygen consumption of the excised roots and their microbial colonizers. Root respiration was subject to diurnal variations. It was low towards the end of the dark period and increased within two hours during the light period. Independent of the nutrient supply the respiration rate and bacterial number were considerably higher in unaerated than in aerated nutrient solution. Root respiration was lowest when using nitrate as a source of nitrogen and highest with ammonium nutrition. Intermediate respiration rates were obtained for mixed nitrogen nutrition. Respiration corresponded to the bacterial colonization of the roots. The discontinuation of potassium supply led in plants supplied with nitrate to an insignificant increase in root respiration, whereas a marked increase in respiration was observed in plants with mixed ammonium and nitrate nutrition. In contrast, Root respiration of plants supplied with ammonium declined when potassium was discontinued. Discontinuation of potassium supply caused an increase in root respiration and bacterial numbers in both aerated and unaerated media.