Spatial distribution and biomass of root nodulesin a naturally regenerated stand of Alnus hirsuta (Turcz.)var. sibirica

摘要

To estimate nodule biomass of Alnus hirsuta var.sibirica, an N2-fixing tree species, we examined thedistribution pattern and size structure of nodules in a 17 to18 year old stand naturally regenerated after disturbance byroad construction in Japan. Nodules were harvested within1 m from the outer edge of stems of plants with differentsizes on four occasions from June to October. The diameterof the subtending root at the base of each nodule and noduledry weight were measured in 20 cm increments outwardsfrom the base of each stem. Horizontal distribution of nodules around each tree varied greatly among tree diametersat 1.3 m (dbh) within the even-aged stand. In particular,smaller individuals had a concentrated distribution of nodulesclose to the stem. Nodule abundance occurred further from thestems with increasing tree size. Nodule biomass within 1 mfrom the outer edge of individual stems increased with treesize ([nodule biomass] = 0.442 [dbh]2.01, R~2 = 0.747, P< 0.05).By using the relationship, nodule biomasses wereestimated to be 84.1 kg ha~(-1). These results suggest thatit is necessary to take into account tree size and patterns oftree distribution in nodule biomass estimates.