While animal and plant diversity has long been understood to be important, the multiple roles of soils – from the decomposition of organic matter to nutrient cycling and carbon fixing – have been less researched.

One of the studies, published in Nature Communications on Thursday, examined microbial diversity in 78 drylands on all inhabited continents and 179 sites in Scotland. It found that the loss of varieties – such as from climate change increasing arid zones – undermined the services the soils provided.

A property at Brewarrina in October 2013:  as much as 75 per cent of Australia is arid.

A property at Brewarrina in October 2013: as much as 75 per cent of Australia is arid. Photo: THE LAND

"As the aridity of soils goes up, the microbial diversity and abundance is reduced," Brajesh Singh, a professor at Western Sydney University and an author of both papers, said. "As the soils' multi-functions are reduced, so there are social and economic consequences."

The second paper, published recently in the Proceedings of the National Academy of Sciences journal found the area of the world's drylands – where rainfall and evaporation rates are roughly balanced – is increasing.

Now covering about 41 per cent of the land surface – and home to a similar share of the world's population – these drylands will increase by at least a tenth by 2100 because of overgrazing, erosion and climate change.

Species other than humans will also be affected by less productive lands.

Species other than humans will also be affected by less productive lands. Photo: Supplied

"Ninety per cent of human settlements in dryland are based in developing countries, posing serious challenges to food security, carbon sequestration and desertification," Professor Singh said.

David Eldridge, a University of NSW-based arid zone specialist and a co-author of the PNAS study, said there is already evidence of "a consistent decline" in the soil microbes and fungi in many regions.

Drylands account for as much as three-quarters of Australia and the functions of soils, including their ability to hold water and withstand erosion, will be affected by diversity loss within them, he said.

Severe degradation of as little as 10-20 per cent of dryland would have an impact on some 250 million people as well as harming the viability of many other species that rely on soil health, from plants to the animals that eat them, Professor Singh said.

While rising carbon dioxide levels – such as from burning fossil fuels – could spur plant growth, such an outcome required available nutrients and water. Those elements, particularly water, that may become less available with climate change, he said.