DENITRIFICATION IN THE RHIZOSPHERE OF RICE AND WHEAT SEEDLINGS AS INFLUENCED BY PLANT K-STATUS, AIR-FILLED POROSITY AND SUBSTRATE ORGANIC-MATTER

The effect of K. deficiency on denitrification in the rhizosphere was studied with wheat and rice plants which are different in aerenchyma formation. The seedlings were grown in carbon-free quartz silt, except for one experiment where cellulose was added. With K sufficient as well as with K deficient plants denitrification increased exponentially, when air-filled porosity of the substrate declined below a threshold of 10-12%. With wheat the increase in denitrification was higher with K deficient individuals. Epidermal and cortical cells of K deficient wheat roots collapsed and became invaded by microorganisms. For rice roots rhizosphere denitrification was generally lower than for wheat roots. K deficient rice roots had not collapsed and did not support higher denitrification in the range of the air-filled porosities tested. Addition of cellulose as a slow-release carbon source enhanced denitrification for K sufficient but not for K deficient rice plants. © 1990.