Life

When it comes to storing carbon in the ground, fungi may be key.

Soils are a massive reservoir of carbon, holding about three times as much carbon as Earth’s atmosphere. The secret behind this carbon storage are microbes, such as bacteria and some fungi, which transform dead and decaying matter into carbon-rich soil.

But not all carbon compounds made by soil microbes are equal. Some can last for decades or even centuries in the soil, while others are quickly consumed by microbes and converted into carbon dioxide that’s lost to the atmosphere. Now, a study shows that fungi-rich soils grown in laboratory experiments released less carbon dioxide when heated than other soils.

The result suggests that fungi are essential for making soil that sequesters carbon in the earth, microecologist Luiz Domeignoz-Horta and colleagues report November 6 in ISME Communications.

Who is making soil matters, Domeignoz-Horta says.

The study comes as some scientists warn that climate change threatens to release more carbon out of the ground and into the atmosphere, further worsening global warming. Researchers have found that rising temperatures can lead to population booms in soil microbes, which quickly exhaust easily digestible carbon compounds. This forces the organisms to turn to older, more resilient carbon stores, converting carbon stored away long ago into carbon dioxide.

With the combined threat of rising temperatures and damage to soil microbe communities from intensive farming and disappearing forests, some computer models indicate that 40 percent less carbon will stick in the soil by 2100 than previous simulations have anticipated (SN: 9/22/16).

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To see if scientists can coax soils to store more carbon, researchers need to understand what makes soil microbes tick. But that is no simple task. “Some say soil is the most complex matrix on the planet,” says Kirsten Hofmockel, an ecologist at the Pacific Northwest National Laboratory in Richland, Wash., who was not involved in the research.

To simplify matters, Domeignoz-Horta, of the University of Zurich, and colleagues grew their own dirt in the lab. The researchers separated fungi and bacteria from forest soil and grew five combinations of these communities in petri dishes, including some that were home only to bacteria or fungi. The researchers sustained the microbes on a diet of simple sugar and left them to churn out soil for four months. The team then heated the different soils to see how much carbon dioxide was produced.

Bacteria were the main drivers behind making soil, but fungi-rich soils produced less carbon dioxide when heated than soils made solely by bacteria, the researchers found. Why is still unclear. One possibility is that fungi could be producing enzymes — proteins that build or break up other molecules — that bacteria aren’t capable of making on their own, Domeignoz-Horta says. These fungi-derived compounds may provide bacteria with different building blocks with which to build soil, which may end up creating carbon compounds with a longer shelf life in soils.

What happens in lab-grown soil may not play out the same in the real world. But the new research is an important step in understanding how carbon is locked away long-term, Hofmockel says. This kind of information could one day help researchers develop techniques to ensure that more carbon stays in the ground for longer, which could help mitigate the amount of carbon dioxide in the atmosphere.

“If we can get carbon in the ground for five years, that’s a step in the right direction,” Hofmockel says. “But if we can have stable carbon in the soil for centuries or even millennia, that’s a solution.” More

When it comes to fidelity, birds fit the bill: Over 90 percent of all bird species are monogamous and — mostly — stay faithful, perhaps none more famously than the majestic albatross. Albatross couples rarely separate, sticking with the same breeding partner year after year. But when ocean waters are warmer than average, more of the birds split up, a new study finds.

In years when the water was warmer than usual, the divorce rate — typically less than 4 percent on average — rose to nearly 8 percent among albatrosses in part of the Falkland Islands, researchers report November 24 in Proceedings of the Royal Society B. It’s the first evidence that the environment, not just breeding failure, affects divorce in wild birds. In fact, the team found that during warmer years, even some females that had bred successfully ditched their partners.

The result suggests that as the climate changes as a result of human activity, higher instances of divorce in albatrosses and perhaps other socially monogamous animals may be “an overlooked consequence,” the researchers write.

Albatrosses can live for decades, sometimes spending years out on the ocean searching for food and returning to land only to breed. Pairs that stay together have the benefits of familiarity and improved coordination, which help when raising young. This stability is particularly important in dynamic, marine environments, says Francesco Ventura, a conservation biologist at the University of Lisbon in Portugal.

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But if breeding doesn’t work out, many birds — mostly females — leave their partner and try to find better luck elsewhere (SN: 3/7/98). Breeding is more likely to fail in years with more difficult conditions, with knock-on effects on divorce rates the following years. Ventura wanted to find out whether the environment also has a direct impact: changing the rate of divorce regardless of whether the breeding had gone well.

Ventura and his team analyzed data collected from 2004 to 2019 on a large colony of black-browed albatrosses (Thalassarche melanophris) living on New Island in the Falkland Islands. The team recorded nearly 2,900 breeding attempts in 424 females, and tracked bird breakups. Then, accounting for previous breeding success in individual pairs, the researchers checked to see if environmental conditions had any noticeable further impact on pairings.

Breeding failure, especially early on, was still the main factor behind a divorce: Each female lays just a single egg, and those birds whose eggs didn’t hatch were over five times as likely to separate from their partners as those who succeeded, or those whose hatched chicks didn’t survive. In some years, the divorce rate was lower than 1 percent.

Yet this rate increased in line with average water temperatures, reaching a maximum of 7.7 percent in 2017 when waters were the warmest. The team’s calculations revealed that the probability of divorce was correlated with rising temperatures. And surprisingly, females in successful breeding pairs were more likely to be affected by the harsher environment than males or females that either didn’t breed, or failed. When ocean temperatures dropped again in 2018 and 2019, so did divorce rates.

Warmer water means fewer nutrients, so some birds may be fueling up out at sea for longer, delaying their return to the colony or turning up bedraggled and unappealing. If members of pairs return at different times, this can lead to breakups (SN: 10/6/04).

What’s more, worse conditions one year might raise stress-related hormones in the birds too, which can affect mate choice. A bird may incorrectly attribute its stress to its partner, rather than the harsher environment, and separate even if hatching was successful, the researchers speculate.

Such misreading between cues and reality could make separation a less-effective behavior, suggests Antica Culina, an evolutionary ecologist at the Netherlands Institute of Ecology in Wageningen who was not involved in the study. If animals divorce for the wrong reason and do worse the following season, that can lead to lower breeding success overall and possibly population decline.

Similar patterns could be found in other socially monogamous animals, including mammals, the researchers suggest. “If you imagine a population with a very low number of breeding pairs … this might have much more serious repercussions,” Ventura says. More

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