Nodule study in Albizia chinensis in relation to nitrogen metabolism, morphology and biomass

Abstract

Morphology, biomass, nitrate reductase (NR) and nitrogenase activity in Albizia chinensis (Osb.) Merr. nodules were assessed on monthly and seasonal basis for 1 year. Average NR and nitrogenase activity was higher during the rainy season, reaching a maximum in August. Thereafter, activity decreased through autumn and reached a minimum value during winter. Fresh and dry biomass of nodules increased gradually from summer to the rainy season and then started decreasing with the onset of winter as nodules began to senesce. Among four developmental stages of the nodules that correspond to their increasing age, NR and nitrogenase activity remained low in stage 1 nodules and peaked in stage 2. The activity of both enzymes further decreased with increasing age (stage 2 to stage 4). Morphological features such as shape, diameter and color varied considerably among the developmental stages. Stage 1 nodules were cream-colored, oval to heart-shaped with smallest average diameter whereas at stage 2, they became bilobed to tetralobed. On the other hand, stage 3 nodules had the largest average diameter and were multilobed in structure. Stage 4 nodules that correspond to the senescing stage were dark brown to black, multilobed, flattened and hollow due to degeneration of nodular tissue.