生物土壤结皮的奥秘

They lie dormant（冬眠，休止） for years, but at the first sign of favorable conditions they awaken. This sounds like the tagline（标语） for a science fiction movie, but it describes the amazing life-cycles of microbial organisms that form the biological soil crusts (BSCs) of Earth's deserts. Now a research team with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) has reported a unique molecular-level analysis of a BSC cyanobacterium responding to the wetting and drying of its environment. The results hold implications for land management, improved climate change models, and a better understanding of carbon cycling in soil microbial communities and how changes in global temperatures impact Earth's deserts. "We found a way to measure from start to finish in real unaltered samples the molecular events behind the response of cyanobacterium to wetting and drying in a desert BSC," says Aindrila Mukhopadhyay, a biologist with Berkeley Lab's Physical Biosciences Division. "Not only did we get a good view of the genetic machinery that wakes the microbes up, but we also got a good sense of what constitutes a healthy BSC."

Mukhopadhyay and Trent Northen, a chemist with Berkeley Lab's Life Sciences Division, are the corresponding authors of a paper describing this research in the journal of the International Society for Microbial Ecology. The paper is titled "Dynamic cyanobacterial response to hydration（水合作用） and dehydration（脱水） in a desert biological soil crust."

Arid and semi-arid deserts make up about 40-percent of Earth's total land mass. Much of the undisturbed soil crust in these deserts is a living mantle of microbes and their by-products, with the predominant inhabitants being cyanobacteria, microorganisms that use photosynthesis for energy. To survive dry spells that can go on for years, BSC microorganisms must enter a dormant state but they must also be poised for rapid resuscitation to utilize short periods of precipitation. For a better understanding of how the microbes are able to do this, the Berkeley Lab research team studied the cyanobacterium Microcoleus vaginatus.

"M. vaginatus is the early BSC colonizer, an ecosystem pioneer that fixes carbon and binds the soil together allowing the community to develop while preventing wind erosion," says Northen. "It is globally distributed in regions where water is scarce, including not only hot deserts but the arctic as well."