2024-05-07 15:24 来源：得道网
气候变化使北极苔原变暖的速度是地球其他地区的四倍。现在，一项研究表明，气温上升将刺激那里的地下微生物产生更多的二氧化碳——这可能会形成一个加剧气候变化的反馈循环。
瑞典尤梅夫大学的环境科学家Sybryn Maes说，冻土带是一个“沉睡的生物群落”。这个生态系统由小灌木、草和地衣组成，它们生长在富含有机碳的寒冷土壤中。长期以来，科学家们一直怀疑气候变暖会唤醒这个沉睡的巨人，促使土壤微生物释放更多的温室气体二氧化碳。但很难在实地研究中证明这一点。
梅斯的团队包括大约70名科学家，他们在地球北极和高山地带的28个冻原地区进行测量。在夏季生长季节，研究人员在冻土带上放置了透明的，顶部开放的塑料箱，每个直径约一米。这些房间让光线和降水进入，但阻挡了风，使里面的空气平均升温1.4摄氏度。研究人员监测了土壤中的微生物向空气中释放了多少二氧化碳，这一过程被称为呼吸作用，并将这些数据与附近暴露的斑块的测量结果进行了比较。
The study, published online April 17 in Nature, found that the 1.4 degree C temperature increase caused an average 30 percent increase in CO2 respiration across the experimental sites compared with the exposed sites. Some of the studies the team compiled lasted only one year, but the longest provided measurements from 25 growing seasons, showing that these effects persist over time.
Though it’s clear that higher temperatures boost CO2 respiration on average, there’s a lot of variability between field sites, Maes says. For instance, the CO2 ramp-up is particularly pronounced in nitrogen-poor soil. As soils warm, plants become more active, and so do their symbiotic microbes, which support the plants by scavenging for nitrogen. The microbes’ heightened activity also means they produce more CO2.
The findings provide the strongest evidence yet that warmer temperatures will increase microbial activity, releasing more CO2, says environmental microbiologist Nicholas Bouskill of Lawrence Berkeley National Laboratory in California. Previous studies, including Bouskill’s own, were much smaller and came to contradictory conclusions.
The long-term question, Bouskill says, is: “Will these areas become carbon sources, or will they remain carbon sinks?”
NASA estimates that the Arctic permafrost stores 1,700 billion metric tons of carbon. Recent studies find that by the year 2100, degrading permafrost could release anywhere from 22 billion to 524 billion metric tons of carbon, depending on the rate of warming.
Given the expected increase in CO2 emissions from microbes and their potential to contribute to further global warming, “you could say this is a doom scenario,” Maes says. But she notes that the study’s results do not mean the tundra’s overall carbon emissions will inevitably skyrocket — other processes may counteract this effect. For example, plants could ramp up their photosynthetic activity, taking up more CO2. And these studies don’t factor in what happens during other times of year.
Incorporating data that captures the nuance of what’s happening in the Arctic — such as the meta between nitrogen-poor soil and microbial respiration — may help improve predictions about the tundra’s response to climate change and how that will, in turn, influence Earth’s climate. “We need to represent how nutrients are cycling in order to get the carbon right,” Bouskill says.
