The response of Albizia adianthifolia to Rhizobium and Nitrogen in forest-grown and greenhouse grown seedlings

Abstract

The wide distribution of Albizia adianthifolia in Ghana, absent from only the wettest sites, combined with its rapid growth and nitrogen fixing capability, makes the species suitable for agroforestry and rehabilitation of degraded sites. We used two isolates of Rhizobium from high and low rainfall forests with the aim of testing for ecotypic differences in the Albizia/Rhizobium symbiosis, as expressed through nitrogen-fixation and nodulation. In forest-grown seedlings, the number of A. adianthifolia seedlings fixing nitrogen did not differ significantly between the two forest types. Conversely, percentage nodulation and nitrogen fixation rates did differ significantly, indicating a greater importance of nitrogen fixation in the dry forest type. A standard nodulation test was set up to assess the effects of Rhizobium inocula from the two forest types on seedlings of A. adianthifolia. Rates of nitrogen-fixation, seedling nitrogen content, number of nodules, seedling mass and root to shoot ratio were measured. Inoculation was found to have a very significant effect on rates of nitrogen-fixation and number of nodules, although no significant effect of the inoculum source was evident. Seedlings were thought to be too young to display any signs of benefiting from inoculation. The well documented effect of combined nitrogen regulating nitrogen fixation was supported.

Keywords: Agroforestry, legume, n-fixation, nodulation

Ghana Journal of Forestry Vol. 17 & 18 2005: pp. 1-8