Cadmium Effects on the Nitrogen Fixation System of Red Alder1
- Carlos Wickliff,
- Harold J. Evans,
- Kevin R. Carter and
- Sterling A. Russell2
Red alder (Alnus rubra Bong.) was grown in sand culture in the greenhouse to obtain data on the effects of cadmium (Cd) on a symbiotic nitrogen (N) fixation system which contributes to the fertility of forest soils. Treatment of red alder seedlings for 11 weeks with 0.545 to 136 µM CdCl2 in N-free nutrient solution decreased in situ nitrogenase activity 25 to 89%, N fixation 23 to 98%, and the number of nodules per plant 29 to 74%, when compared to plants receiving no Cd. Similar reductions were observed in plant growth. Treatment with 0.054 to 0.545 µM CdCl2 decreased nitrogenase activity 6 to 31%.
When non-nodulated A. rubra seedlings were inoculated in the presence of 0.054 and 0.109 µM CdCl2, N fixation decreased 52 and 89%, respectively. Plant growth decreased in a similar fashion. When non-nodulated seedlings were given 0.545 µM CdCl2 and 6 mM NH4NO3 or Ca(NO3)2, nitrate reductase activity decreased 22 and 24%, respectively, when compared to plants receiving no CdCl2. Nitrogen accretion and plant dry weights were decreased by treatments in which plants were supplied with Ca(NO3)2 and 0.273 and 0.545 µM CdCl2, when compared to controls without CdCl2.
These results suggest that Cd can inhibit nitrogenase activity and therefore N fixation. Growth, nodulation, and nitrate reductase activity are also inhibited by Cd.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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