Rhizobia are a "group of soil bacteria that infect the roots of legumes to form root nodules". Rhizobia are found in the soil and after infection, produce nodules in the legume where they fix nitrogen gas (N2) from the atmosphere turning it into a more readily useful form of nitrogen.
I believe it is 'white fur' because living in the Tundra means it is snowing. Snow is white, so basically, the white fur is specifically for the Tundra.
