Nitrification in the rhizosphere of a flooding-resistant and a flooding-non-resistant Rumex species under drained and waterlogged conditions

Abstract

The effects of the flooding-resistant plant species Rumex palustris and the non-flooding-resistant plant species Rumex acetosa on nitrification were compared. The plants were grown under drained and waterlogged conditions on a mixture of calcareous riversand and sieved grassland soil with a high potential nitrifying activity. In the shoots of R. acetosa, but not in those of R. palustris, the ratio between the amounts of accumulated carboxylates and organic nitrogen, ((CA-A)/N org.), appeared to be a useful indicator of ammonium or nitrate consumption by tghe plant. In both plant species, the inorganic nitrogen source had no observed effect on the (C-A)/N org. ratio in the roots. The growth of R. acetosa, but not that of R. palustris was inhibited by waterlogging of the soil. Both the activity and the growth of the ammonium-oxidizing bacteria were repressed under drained and waterlogged conditions in soils with R. palustris, a condition that was attributed to a competitive ammonium uptake by its relatively fast growing roots. In the presence of R. acetosa, the activity and growth of the ammonium-oxidizing bacteria were inhibited under waterlogged, but not under drained, conditions. he growth and activity of nitrite-oxidizing bacteria in the absence of actively ammonium-oxidizing, nitrite-producing bacteria was likely due to organotrophic growth.