Denitrification in the rhizosphere of plants with inherently different aerenchyma formation: Wheat (Triticum aestivum) and rice (Oryza sativa)

Abstract

Denitrification in the rhizosphere of wheat and rice was studied in relation to aerenchyma formation. Seedlings were grown in quartz silt amended with mineral nutrients at given bulk densities and water tensions. In adventitious wheat roots the formation of cortical lacunae was strongly dependent on soil aeration. Growing the wheat plants in dry (−20 kPa) and moist substrate (−2 kPa) established aerenchyma contents of 3% and 15%, respectively. Denitrification was measured after the introduction of equal moisture levels in the substrates of both treatments. The higher aerenchyma content of roots pregrown in the wetter substrate did not counteract denitrification in the rhizosphere which had doubled in this treatment. In contrast to the unspecific lysis of cortical cell walls, the well organized formation of aerenchyma in rice roots was independent of soil aeration. Root porosity averaged 14%. As in wheat, it was not related to denitrification. However, the level of denitrification per mg of root dry matter was about four times lower than that of wheat. The addition of decomposable organic matter (cellulose) to the substrate stimulated aerenchyma formation in rice and considerably increased denitrification. The results suggest that denitrification in the rhizosphere is independent of aerenchyma formation.