10 July 2023

Chinese study unravels the mysteries of biocrusts


Researchers have shown how surface biocrusts protect subsoil microorganisms by increasing their diversity and stability which benefit the soil

by Matteo Cavallito


Widespread in arid or semi-arid lands, soil biocrusts are a particularly valuable natural resource. Crucial in fact is the role of its hosts, namely fungi, lichens and microbes. These communities of microorganisms are the ones that maintain the function of ecosystems. But the dynamics behind them are still unclear.

Unraveling part of these mechanisms is a recent study by the Chinese Academy of Sciences that sequenced long-term restoration processes in the southeastern edge of the Tengger Desert. The researchers, led by scientist Li Xinrong of the Academy’s Northwest Institute of Ecoenvironment and Resources, highlighted the drivers of changes in subsurface bacterial communities. And the influence played by the crusts above them.

Biological crusts are a crucial junction between soil and atmosphere

“Biocrusts cover approximately 30% of the global dryland surface area, constituting a crucial atmosphere–soil interface,” says the study published in the journal Plant and Soil. “Bacteria living at this interface participate in almost all biogeochemical cycling processes that may profoundly alter soil and ecosystem multifunctionality and speed up ecosystem restoration.”

The researchers, says a statement by the Chinese Academy of Sciences, conducted molecular-level analyses to reveal the relationships between the diversity, complexity and stability of soil bacterial communities and the changes detected in both the crust and subsurface layers. In both layers, the study showed, bacterial diversity and dissimilarity increased as vegetation was restored over time, positively impacting soil quality and function.

The study

By analyzing the successions of strata and related bacteria, lichens and mosses over a period of 65 years, scientists observed changes in the diversity of microorganisms at the surface and at depth. “In particular, the subsoil bacterial network properties, including nodes, links, average links per node, average clustering coefficient, connectance and relative modularity, were significantly higher than those of biocrust in late succession.”

The investigation thus demonstrated the ability of the crust to influence the characteristics of the subsurface bacterial community.

The scientists found “that succession, soil physicochemical conditions, and biocrust bacterial community composition were the strongest direct drivers of subsoil bacterial community composition.” Moreover, “The plant communities and biocrust bacterial community composition directly drove the network complexity and stability of the subsoil bacterial community.”

The world is at risk of losing up to 40 percent of its crusts

What emerges, in short, is the importance of biological crusts in protecting subsurface microorganisms by promoting their increased diversity and stability to the benefit of the soil itself. In light of all this, the widespread concern about the health of these peculiar surface layers of soil assumes even greater significance. Biocrusts, in fact, appear to be in danger.

Early last year, a research by the U.S. Geological Survey highlighted how climate change is impacting the crusts themselves.

Analyzing some surface areas in the expanses of Canyonlands National Park, Utah, scientists recorded a dramatic decline in the presence of lichens, a phenomenon linked to rising temperatures that threatens the survival of the crust. In the absence of global climate mitigation strategies, the authors concluded, the world risks losing 25 percent to 40 percent of its crusts by 2070.