The Physiology of Spore-Negative and Spore-Positive Nodules of Myrica gale

Document Type

Article

Journal/Book Title

Plant and Soil

Publication Date

1-1-1989

Volume

118

First Page

75

Last Page

87

Abstract

The physiology of spore-negative and spore-positive root nodules was investigated in Myrica gale L. grown in water culture in a growth chamber. Spore(−) nodules were induced with Frankia cultures and spore(+) nodules with crushed nodules. Gas exchange was measured in a flow-through system.

The time course of acetylene reduction following addition of acetylene was essentially the same in both spore(−) and spore(+) nodules with a stable maximum between 2 and 4 minutes followed by a steep decline to a minimum (37% of the maximum) between 9 and 30 minutes depending on the plant. The minimum was followed by a partial recovery. Nodule CO2 evolution showed a similar pattern but the minimum rate (83% of the maximum) was not nearly as low.

Plants nodulated with one spore(−) and one spore(+) strain were compared at 6, 8 and 10 weeks after inoculation. At 6 weeks the spore(−) plants had 52% greater specific nitrogenase activity and 46% more biomass than the spore(+) plants. At 8 and 10 weeks, however, the differences between plants with spore(−) and spore(+) nodules became smaller.

Plants nodulated with 4 spore(−) and 5 spore(+) strains were compared at 8 weeks after inoculation. Collectively the spore(−) plants exhibited a 32% greater specific nitrogenase activity, a 15% lower energy cost of nitrogenase activity (CO2/C2H4), and invested 31% less biomass in nodules than the spore(+) plants. The spore(−) plants also produced 16% more biomass indicating that spore(−) strains are generally more desirable than spore(+) strains. However, two spore(+) strains were as effective as the spore(−) strains.

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