Ever stop to think about the worlds of life to be found in the leafy canopy above your head?

University of California, Riverside Environmental Science Professor, David E. Crowley, took that approach when examining the tropical rainforest canopy of Brazil and found an extraordinary amount of previously unknown bacterial biodiversity living among the leaves.

His findings can be found in today's edition of the journal Science in a paper titled "Bacterial Diversity in Tree Canopies of the Atlantic Forest," co-written with Brazilian colleagues M.R. Lambais, J.C. Cury, R.C. Büll and R.R. Rodrigues.

"The basic discovery is that every tree species selects for its own microbial community, which consists of several hundred bacterial species on each tree species," Crowley said. "Almost all are new species and genera, and some even represent new families and divisions of bacteria."

Analysis of bacterial 16S ribosomal RNA gene sequences revealed that about 97 percent of the bacteria were unknown species and that the phyllosphere (the leafy world of a plant) of any one tree species carries at least 95 to 671 bacterial species.

Estimates for the 20,000 or so vascular plant species in the Atlantic forest could mean the discovery of between 2 and 13 million new microbial species. By contrast the Earths oceans are thought to contain up to 2 million species and a ton of soil may have 4 million species, according to the paper. Then there's the question of the role these microorganisms play in the ecosystem. Do they defend the plant against herbivores or pathogens? Do they play a purely symbiotic or a parasitic role?