Why this crucial building block of protein is disappearing from Earth's soil
Nitrogen — the seventh element on the periodic table — is an essential ingredient for many fundamental biological processes. That’s why it’s big news that nitrogen is increasingly unavailable in ecosystems across the world.
In a first-of-its-kind analysis, a group of researchers with a wide range of specialties analyzed more than a century’s worth of data to reach the stunning conclusion. Their results were published Thursday in the peer-reviewed journal Science.
“There is a fairly large-scale decline in nitrogen availability that… seems to have started sometime around the early twentieth century and appears to be ongoing,” environmental researcher Rachel Mason, a co-author of the new paper, tells IE.
Many factors — from wildfires and climate change to industrialized agriculture — are driving the change. Mason says the findings underscore the complexity of the nitrogen cycle and the broader Earth system.
“The Earth's system is complicated, and we are poking it in so many different ways,” she says.
Several mechanisms are driving the change
Most environmental concerns about nitrogen have focused on an overabundance of the element, not a lack of it. “Before I got involved in this work, I would just have thought, yeah, nitrogen is a problem because there's too much of it,” Mason says. “That's absolutely true if you're talking about agricultural areas and the lakes and oceans downstream from [them].” In the Gulf of Mexico, for example, excess fertilizer causes algal blooms that create to “dead zones” of very limited biodiversity.
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But on land, there’s an entirely different set of problems that drain accessible nitrogen far more quickly than it can be replaced.
One example is the intensive grazing of livestock. “We export cattle full of protein out of grasslands,” Mason says. Just as agricultural regions in California export an incredible amount of water in the form of produce, states with significant beef industries end up exporting a lot of the nitrogen from their soil as meat. “In a protein molecule, one atom out of every six is nitrogen,” Mason says.
Wildfires are another driver. “You can lose a lot of nitrogen during fires, which seemed to be becoming more frequent and more intense in some areas,” Mason says. Climate change is also affecting how much nitrogen is being put back into the soil through natural processes. “Changes in temperature and the length of the growing season, local microclimates, and freeze-thaw cycles [are having] effects on microbial and plant processes [that fix nitrogen],” she says.
Higher concentrations of carbon in the atmosphere may also play a role. The extra CO2 “can cause nitrogen to get locked up in organic matter in a way that makes it unavailable to [other] plants,” Mason says.
The lack of nitrogen is becoming a serious problem
Nitrogen — along with oxygen, carbon, hydrogen, phosphorous, and sulfur — is necessary for life. For instance, it's an indispensable part of photosynthesis. “You need nitrogen to produce chlorophyll,” Mason says. It’s a fundamental building block of protein, too.
“Declines in nitrogen availability basically translate into the availability of plant proteins for insect herbivores and grazing mammals. [It] may well have effects on the growth and reproduction of those creatures,” Mason says.
It’s difficult to track how declining levels of available nitrogen have affected livestock productivity because ranchers are constantly changing the genetics of livestock to produce more, “but at some point… you might end up finding that they just don't [get] as much food from their livestock as they used to," Mason says.
Declining levels of nitrogen are certainly expensive for livestock producers. According to one estimate, ranchers have invested billions of dollars in extra feed to make up for lost protein. There's also reason to think that insects are suffering from the change to these ecosystems.
"It totally makes sense that declining nitrogen availability could be one of the driving forces behind the so-called insect apocalypse. Insects are so important to ecosystems that we don't want all the insects to go away," she says.
Understanding the nitrogen cycle is complicated
Mason says it’s difficult to way what these declining levels of nitrogen mean for the future.
“Actually predicting those effects gets really complicated because everything interacts with everything else,” she says. What’s important to remember is that it's not a question of whether there is too much nitrogen or too little.
“We put pressure on the Earth systems in so many different ways that we're going to end up with a really complicated and sometimes counterintuitive set of problems [that] might look completely different in one location [when] compared to another,” she says.
“We'd like this to foster more of a recognition that the Earth's system is complicated,” she says.
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