Nitrogen Fixation and Nodulation Behaviour in Relation to Seasonal Changes in Six Multipurpose Tree Species

Six multipurpose, nitrogen fixing tree species viz., Acacia nilotica. An evergreen, dry zone and Robinia pseudo-acacia, deciduous. Temperate, both spiny medium sized tree species. Albizia lebbek, Dalbergia sisoo fairly large and Ougeinia oojeinensis middle sized deciduous tree of sub-tropical climate upto 1200 m. sub-Himalayan tract and Pongamia pinnata, evergreen, medium sized. Tree widely distributed throughout the country. These species have been used for the various afforestation programmes in the country. The seedlings of these species were raised in Plant Physiology Branch, Botany Division,Forest Research Institute, Dehra Dun, to study the seasonal variation effects on nodulation behaviour and nitrogenase (acetylene-ethylene reduction) activity. In three species viz., Acacia, Ougeinia, Robinia, maximum nitrogenase activity was observed during summer season, whereas, in other three species i.e. Albizia, Dalbergia, Pongamia during rainy season. However, lowest activity in most of the species was recorded during winter season. Maximum nodule number per plant was reported during rainy season except Robinia in summer. An identical trend in nodule growth and nitrogen fixation activity was recorded in Dalbergia and Ougeinia seedlings. Whereas, Acacia, Albuizia and Pongamia have followed almost similar trend among themselves for nodule number and nodule biomass. This study concludes that the nodulation and nitrogen fixation behaviour differs within and between species and seasons.