Botany 101 Bonus

 

Japanese Pagoda trees are in the legume family, along with peas and beans (and the Sunburst honey locusts and redbuds in the Park, with similar pea-like seed pods). Most legumes have nodules containing bacteria in their roots. Even though our atmosphere is 80% nitrogen, plants are unable to use gaseous nitrogen to build the molecules they need for life. The bacteria in the nodules and elsewhere in the soil take the nitrogen in the air and convert it into molecules like ammonia that the plants can then use. Having the bacteria in high concentrations and close by in the nodules increases the nitrogen concentration in the soil around the roots. The bacteria benefit by having a secure home and taking carbon compounds from the plant. In the days before synthetic fertilizers, legumes like soybeans were planted in fields and then plowed under to increase the nitrogen content of the soil.

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In biology there are always exceptions to general rules. The Japanese Pagoda tree is an exception in that it is a legume that has no nitrogen-fixing bacteria nodules.

 

Symbiosis is a relationship between organisms in which both organisms benefit. The relationship of legumes with nitrogen-fixing bacteria is another example of symbiosis, similar to that of fungi living intertwined with the roots of most trees. The fungi supply another essential element, phosphate, to the plants, and receive carbon compounds from the roots.