Altitudinal variation in nitrogenase activity of the Himalayan alder naturally regenerating on landslide‐affected sites

Abstract

SUMMARYNatural regeneration, root nodule biomass and nitrogenase activity (acetylene reduction) of Alnus nepalensis D. Don (alder) were estimated at ten different landslide‐affected elevated (1000–2500 m) sites in the Kalimpong forest division of the Eastern Himalayas. Alder regeneration was best in the middle zone (1500–2000 m) of this altitude range. Nitrogenase activities were between 5 and 19 μmol C2H4 g−1 nodule d. wt h−1 in a peak activity month (July). The activity was largely dependent on mean soil temperature and root nodule moisture. The highest rate of acetylene reduction was found in the rainy season (July) at the 1830 m elevation site. Nitrogenase activity was negligible at night and increased during the day with a midday maximum. Alder regeneration, seedling growth, root nodule biomass and nitrogenase activity were temperature dependent along the gradient of altitude and fell off below 1500 m and above 2000 m.