Black Locust & Drought – Field Study Suggests that Drought Diminishes its Nitrogen-Fixing Ability

By Sarah Farmer, USDA Forest Service Southern Research Station

Black locust (Robinia pseudoacacia)With its symbiotic bacteria, black locust (Robinia pseudoacacia) makes its own nitrogen fertilizer – and can share it with other tree species.

“In early successional temperate forests, symbiotic nitrogen fixation is often the main source of new nitrogen,” says USDA Forest Service scientist Chelcy Miniat.

But drought could slow the rate of symbiotic nitrogen fixation, according to a recent study led by Jeffrey Minucci, a Ph.D. student at the University of Georgia at the time of the research. Miniat contributed to the study, and the results were published in the journal Ecology.

Black locust is relatively drought-tolerant, but when water is scarce, sugars are more difficult to make. And sugars are what black locust provides to its symbiotic nitrogen-fixing bacteria. Black locust can allocate more or less sugar to its symbiotic bacteria, but even if it provides less to them during drought, it may be at a competitive disadvantage.

The three-year field study took place on the Nantahala National Forest in western North Carolina.

In 2010, about 75 percent of the trees were harvested. The remaining trees provided seeds for the next generation, and the silviculturists on the Nantahala Ranger District painted the stumps of harvested trees with herbicide so that seeds would come from tulip poplar (Liriodendron tulipifera) and oak species (Quercus spp.). Black locust is an early successional species and was probably rare in the study plots before harvest, but it is such a dependable colonizer of disturbed areas that some people in the South think of it as a weedy tree.

Read more here:

Read the article in Ecology: