Utilization of rhizobia by the invasive legume, sericea lespedeza (Lespedeza cuneata)

Abstract

In the late 1800s, Lespedeza cuneata (sericea lespedeza) was introduced in North America. It became a noxious weed in Kansas due to its ability to invade and degrade native tallgrass prairie, and is currently one of the largest threats to existing tallgrass prairie. Because L. cuneata is a legume and is not native to North America, it must utilize existing rhizobia available in its environmentbecause when a legume is transported to new locations as seed, the rhizobia that it normally utilizes are not transported with it. Previous studies have suggested that some legumes are highly specific, allowing a limited number of rhizobia species to form symbioses while other legumes are highly promiscuous. It was not clear if this was the case with L. cuneata in Kansas. In this study, the bacteria in the root nodules of L. cuneata were identified. Three species of rhizobia were found occupying the root nodules, Bradyrhizobium liaoningense, Bradyrhizobium betae and Mesorhizobium caraganae. The effects of B. liaoningense and B. betae on L. cuneata growth were tested in greenhouse grown plants. The results suggested that L. cuneata was relatively specific to the rhizobia species it allowed to infect its roots and Bradyrhizobium could improve L. cuneata growth. The relationship between M. caraganae with L. cuneata is uncertain.Future control of this invasive plant might be developed by creating a mechanism to block the infection pathway between L. cuneata and Bradyrhizobium specifically.