Nodulation and growth of mycorrhizal Casuarina equisetifolia JR. and G. First in response to flooding

The influence of vesicular-arbuscular mycorrhizal (VAM) inoculation on nodulation and growth of flooded Casuarina equisetifolia J.R. and G. First was investigated. Casuarina seedlings were grown in sterile soil inoculated with Glomus clarum Nicolson End Schenick and flooding was imposed for 8 weeks. Mycorrhizal Casuarina seedlings adapted to flooding better than non-inoculated seedlings. This was achieved partly by the greater development of adventitious roots and hypertrophied lenticels which increased oxygen availability, and therefore VAM infection in the upper soil zone. The VAM infection led to the suppression of the accumulation of toxic products of anaerobic respiration, such as ethanol. Mycorrhizal inoculation also prevented the total suppression of nodulation in the flooded plants. Nodulation was observed only in upper soil zone, and its occurrence made dinitrogen fixation possible. The results suggest that mycorrhizal infection is essential for nodulation of Casuarina in flooded soils and is therefore related to the relatively higher dinitrogen accumulation in Casuarina under anoxic conditions.