© 1991 Heron Publishing—Victoria, Canada
Allometry of acetylene reduction and nodule growth of Robinia pseudoacacia families subjected to varied root zone nitrate
concentrations
Kurt H. Johnsen (1, 2) and Bruce C. Bongarten (1)
1. School of Forest Resources, The University of Georgia, Athens, Georgia 30602, USA / 2. Forestry Canada, Petawawa National Forestry Institute, Chalk River, Ontario, Canada, K0J 1J0 / Received December 20, 1990
Summary
The effects of nitrate (NO3–) on acetylene reduction and growth were examined in nodulated seedlings from three open-pollinated families of black locust
(Robinia pseudoacacia L.) grown in sand culture. In the first study, nine-week-old seedlings were supplied with 0.0, 0.5, 1.0, 5.0 or 15.0 mM NO3–, for two weeks during which acetylene reduction and biomass were measured five times. In the second study, eight-week-old
seedlings were supplied with 0.0, 1.0 or 5.0 mM NO3– for 51 days during which acetylene reduction and biomass were measured six times. Results were analyzed with and without
adjustments for seedling size. In the first study, 15.0 mM NO3– significantly decreased total acetylene reduction but lower concentrations did not. In seedlings given 15.0 mM NO3–, both nitrogenase activity and nodule biomass were reduced. Inhibition of nitrogenase activity by NO3– was reversible. In the second study, both the 1.0 and 5.0 mM NO3– treatments increased plant growth compared to the control (0.0 mM). At the end of the 51-day treatment period, total acetylene
reduction and nodule biomass were greatest in the 1.0 mM NO3– treatment and least in the 5.0 mM NO3– treatment. However, when adjusted for seedling size, total acetylene reduction and nodule biomass were similar in the 0.0
and 1.0 mM NO3– treatments. The greater total acetylene reduction and nodule biomass of seedlings grown with 1.0 mM NO3– resulted from increased seedling size due to fertilization. After adjustment for plant size, total acetylene reduction, nodule
biomass and nitrogenase activity were significantly lower in the 5.0 mM NO3– treatment compared with the control or 1.0 mM NO3– treatment. Adjustment for seedling size, by means of allometric principles, appears necessary to interpret treatment effects
on total acetylene reduction and its components, nodule biomass and nitrogenase activity correctly.
