Why are the Grasses Green in Alpine Meadows?

Soil samples from the rhizosphere of Poa alpina and Trisetum spicatum collected on Lookout Mountain, Banff National Park, Alberta contained at least 10 times more bacteria than the soil 3 cm away. The number of bacteria counted on nitrogen
free growth media ranged from 5 to 56% of the total heterotrophic count on a minimal (R2A) media.  Consistently more nitrogen fixing bacteria were isolated from the P. alpina rhizosphere compared with T. spicatum despite their close proximity (<l m).  The microorganisms that readily grew on nitrogen free medium after six successive transfers were identified
to be Xanthobacter flavus, X. autotrophicus, Azotobacter beijerinckii, Azomonas macrocytogenes, Flavobacterium multivorum, Flavobacterium aguatile and Beijerinckia indica. P. alpina seedlings inoculated with nitrogen fixing bacteria in vitro remained green and healthy for a much longer time than the uninoculated seedlings when grown in nitrogen free medium. Scanning electron micrographs of the roots of these inoculated seedlings and bulbils planted in Lookout Mountain soil revealed their close association with the bacteria.