According to the latest report, nitrogen is one of the most important elements on earth. It is a major component of the air we breathe, a major building block of protein, and an important source of fertilizers, playing a pivotal role in the food supply for the global population.
But in recent decades, experts in multiple disciplines have begun to warn that the amount of nitrogen available in global ecosystems is dwindling. According to a review of studies published in Science this week, the trend is linked to anthropogenic climate change that could have “long-term effects.”
Scientists have been noticing this for a while, and some evidence has been observed in experiments, but it’s scattered across different fields. While more and more people are becoming aware that available nitrogen levels are decreasing, this problem has been ignored to a certain extent as more people are grappling with the opposite problem of excessive nitrogen pollution.
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Moreover, industrial and agricultural activities have doubled the global abundance of reactive nitrogen, causing nitrogen to often infiltrate ecosystems with a range of negative effects, such as increasing the formation of low-oxygen waters, promoting harmful algal blooms, and reducing biodiversity, etc.
Much attention has been given to alleviating the problem of excessive nitrogen levels in certain ecosystems. But the paper published this time hopes to warn of another trend: It is not a left-to-right problem that nitrogen in other ecological niches is decreasing due to anthropogenic factors.
Yes, the problem of excess nitrogen does exist, but there is another problem that needs our attention. There are still many unanswered questions about whether the nitrogen supply is more or less.
But what we do know is that this problem, like many others, is also related to the use of fossil energy by humans. Greenhouse gases from human activities continue to enter the Earth’s atmosphere, driving atmospheric carbon dioxide levels to their highest levels in millions of years.
As a result, surface plants breathe 50 percent more carbon dioxide today than they did 150 years ago. Because carbon dioxide acts as a “fuel” for plants, many plants grow faster in new conditions. But experiments and field studies have shown that nitrogen availability cannot keep up with this accelerated growth, resulting in a dilution of nitrogen in plants. The impact will ripple through the entire ecosystem.
Humans are adding more carbon to the ecosystem, which acts as a natural fertilizer for plants. Plants absorb carbon dioxide and then perform more photosynthesis. But with the exception of some areas affected by agriculture and industry, nitrogen levels in ecosystems have not increased year on year, creating this carbon-nitrogen imbalance.
Plants absorbing the carbon dioxide we emit is a good thing because it offsets some of the emissions and provides a little mitigation for climate change, but if plants continue to do a lot of photosynthesis under the influence of carbon dioxide, they need more nitrogen to Carry out activities such as synthesizing chlorophyll. Chlorophyll synthesis is the first step in photosynthesis. Without enough nitrogen, plants cannot carry out these activities and the carbon dioxide we emit cannot be offset.
This imbalance hinders the normal flow of nitrogen between habitats, and there is an overall reduction in the amount of nitrogen available to nitrogen-demanding life forms. But the problem isn’t just the ratio between nitrogen and carbon dioxide. Wildfires associated with climate change also further reduce nitrogen levels in ecosystems. As a 2017 study found, frequent savannah and broadleaf forest fires have reduced soil nitrogen levels by nearly 40 percent over the past 60 years.
While the macro impact of these factors is not fully understood, the paper published this week suggests that plants with less nitrogen may not be able to provide enough nutrients for the many species that depend on them, such as insects and herbivores. Ecosystems are already in turmoil under human-induced changes that will bring new instability to ecosystems.
