Seasonal changes in nodular nitrogenase activity of Alnus glutinosa and Elaeagnus angustifolia

Root nodule development, and seasonal patterns of nodular nitrogenase and hydrogenase activities were determined for 5- to 8-year old black alder (Alnus glutinosa (L.) Gaertn.) and Russian olive (Elaeagnus angustifolia L.) interplanted with black walnut (Juglans nigra L.) on bottomland and upland sites in central Illinois, USA. Black alder produced nodules at both sites, but Russian olive did so only at the bottomland site. Nodular nitrogenase activity was detectable in both species over a 220-day period. Maximum, midday rates of nitrogenase activity (acetylene reduction) of 15 to 20 micromoles C(2)H(4) per g dry nodule per hour were maintained by black alder for approximately 150 days at both the upland and bottomland sites. Near maximum rates of nodular nitrogenase activity were maintained for a similar period by Russian olive at the lowland site, although specific nitrogenase activity was approximately 25% lower than in black alder owing to a larger proportion of necrotic nodular tissue in Russian olive. In both species, nitrogenase activity increased exponentially with temperature between 10 degrees C and 20 to 25 degrees C. No net hydrogen evolution by nodules of either species was detected at any time during the assay period, indicating efficient hydrogenase systems were operating under the conditions of the field assay. Height of black walnut interplanted with nodulated black alder and Russian olive was greater than that of black walnut grown in pure stands.