From
Tropics to Poles: Groundbreaking Study Reveals for First
Time True Diversity of Life in Soils Across the Globe, New
Species Discovered
TAMPA- Microscopic animals that live in soils are
as diverse in the tropical forests of Costa Rica as they are in
the arid grasslands of Kenya or the tundra and boreal forests of
Alaska and Sweden, according to a groundbreaking study appearing
today in the Proceedings of the Natural Academy of Sciences.
Scientists have generally accepted that a wider range of species
can be found above ground at the equator than at the Earth’s
poles, but this study proves for the first time that the same
rules don’t apply to the nematodes, mites and springtails living
underground. The full report is available at http://www.pnas.org/content/early/recent
.
The team of National Science Foundation-funded ecologists on the
study includes Tiehang Wu and Jim Garey at the University of
South Florida, Diana Wall at Colorado State University, Ed Ayres
now at Neon Inc. in Colorado and Richard Bardgett at the
University of Lancaster in the United Kingdom.
This is the first comprehensive molecular analysis - at nearly a
species resolution - of the global distribution of soil animals
across a broad range of ecosystems from the tropics to the
poles. Soil samples were taken from 11 sites around the world,
including tropical forest in Costa Rica, arid grassland in
Kenya, warm temperate forest in New Zealand, shrub steppe of
Argentina, and tundra and boreal forest of Alaska and Sweden.
Through DNA testing, researchers found each location had a
diversity of soil animals, but each ecosystem is unique with its
own soil animals – mostly illustrating an “amazing diversity of
species” that had never been discovered before, said Garey,
chair of the Department of Cell Biology, Microbiology and
Molecular Biology at the University of South Florida.
“On average, 96 percent of our identified soil animals were
found at only a single location, suggesting most soil animals
have restricted distributions, or in other words, they are
endemic,” said Wall, a University Distinguished Professor in
biology at Colorado State. “This challenges the long-held view
that these smaller animals are widely distributed. However,
unlike most above-ground organisms, there was no indication that
the location made a difference in soil animal diversity.”
“Mites and roundworms dominate soil ecology and contribute to
the breakdown and cycling of nutrients in the soil,” Garey said.
“These animals are essential to the proper function of the soil
ecosystem in natural and farm land.”
The study also examined how the global distribution of soil
animals relates to factors such as climate, soil nutrient
levels, and above-ground biodiversity.
Results showed sites with greater above-ground biodiversity
appeared to have lower diversity beneath them in soil. The main
factors explaining this low soil animal diversity at sites with
high aboveground diversity were high levels of soil inorganic
nitrogen availability and lower pH compared with other sites.
Some sites with high animal biodiversity, like the Kenyan
grassland site, are considered more at risk due to land use and
population increase.
PHOTOS
Springtail, a common soil animal
(photo
courtesy of Val Behlan-Pelletier).
Soil mite, a common soil animal
(photo
courtesy of Val Behlan-Pelletier).
Jim Garey loads a sample into a
DNA Sequencer at the University of South Florida.
(photo courtesy of Jim Garey)
Tiehang Wu analyzes soil
DNA in the laboratory. (photo courtesy
of Jim Garey)
Ed Ayres and Diana Wall measure soil respiration of soil in a
Kenya grassland. (photo
courtesy of Diana Wall)
Jim Garey in the Costa Rican Rainforest, one of the soil
locations described in the article. (photo
courtesy of Jim Garey)
JOURNAL: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES:
TITLE: A molecular study of the worldwide distribution
and diversity of soil animals.
AUTHORS: Tiehang Wu1, Edward Ayres2†, Richard D. Bardgett3,
Diana H. Wall2,4 & James R. Garey1*
1Department of Cell Biology, Microbiology and Molecular
Biology, University of South Florida, 4202 East Fowler Avenue,
Tampa, FL 33620, USA
2Department of Biology and Natural Resource Ecology
Laboratory, Colorado State University, Fort Collins, CO 80523,
USA
3Soil and Ecosystem Ecology Laboratory, Lancaster Environment
Centre, Lancaster University, Lancaster LA1 4YQ, UK
4Department of Biology, Colorado State University, Fort
Collins, CO 80523, USA
Technical Abstract from the Article
The global distribution of soil animals and the
relationship of below-ground biodiversity to above-ground
biodiversity are not well understood. We examined 17,516
environmental 18S rRNA gene sequences representing 20 phyla of
soil animals sampled from 11 locations covering a range of
biomes and latitudes around the world. No globally cosmopolitan
taxa were found and only 14 of 2,259 Operational Taxonomic Units
(OTUs) found were common to 4 or more locations. Half of
those were circumpolar and may reflect higher connectivity among
circumpolar locations compared to other locations in the
study. Even when OTU assembly criteria were relaxed to
approximate the Family taxonomic level, only 34 OTUs were common
to 4 or more locations. A comparison of our diversity and
community structure data to environmental factors suggests that
below-ground animal diversity may be inversely related to
above-ground biodiversity. Our data suggests that greater soil
inorganic N and lower pH could explain the low below-ground
biodiversity found at locations of high above-ground
biodiversity. Our locations could also be characterized as being
dominated by microarthropods or dominated by nematodes.
Locations dominated by arthropods were primarily forests with
lower soil pH, root biomass, mean annual temperature, low soil
inorganic N and higher C:N, litter, and moisture compared to
nematode dominated locations which were mostly grasslands.
Overall, our data indicates that small soil animals have
distinct biogeographical distributions and provides new evidence
of the link between above-ground and below-ground biodiversity
at a global scale.
