Nitrogen Fixation in the Coralloid Roots of Macrozamia Communis L. Johnson

Abstract

Coralloid roots of Macrozamia communis have been shown by the isotopic method to fix nitrogen when they contain the endophytic blue·green algae. Immature coralloid roots devoid of the endophyte did not fix nitrogen. Coralloid roots from glasshouse-grown plants fixed 2· 7 times as much nitrogen when illuminated than they did in the dark and the IfiN excess was about equally divided between fractions soluble or insoluble in 3N HCI. Coralloid roots excavated from beneath large fieldgrown plants were opaque and did not fix more nitrogen when illuminated than they did in the dark. Most of the newly fixed nitrogen was found in the buffered sucrose extract of crushed tissue. When an intact plant bearing coralloid roots was exposed to an atmosphere containing a large excess of IfiN. for 48 hr the IfiN was found to be distributed through the plant parts. Nitrogen fixed in the coralloid roots is thus available for the growth of the plant. The coralloid roots evolved small amounts of hydrogen.