Following rain, desert microbes exhale potent greenhouse gas

Date:
March 9, 2022
Source:
University of California - Riverside
Summary:
New research shows how, after it rains, microbes in desert soil
convert one form of pollution into another -- laughing gas.



FULL STORY ==========================================================================
New UC Riverside research shows how, after it rains, microbes in desert
soil convert one form of pollution into another -- laughing gas.


==========================================================================
No laughing matter, nitrous oxide or N2O is the third most potent
greenhouse gas. Scientists conducting the research were surprised to
measure N2O production in the desert heat.

"It only happens in waterlogged soils. Since the desert is dry most of the year, we didn't think this process could occur in arid soils," said Alex Krichels, UCR environmental scientist and first author on the new study.

This study, published in the journal Biogeochemistry, examines how and
why desert-dwelling bacteria are producing N2O emissions. It builds
on work published in 2020, when a team led by UCR landscape ecologist
Darrel Jenerette found desert soils produce substantial amounts of N2O
after a rain.

The traditional view, Krichels explained, is that N2O comes from heavily fertilized agricultural fields like those in the Midwest. Growers add
more nitrogen, ammonium and nitrates than plants need, and after a rain, bacteria convert the excess into N2O, a process called denitrification.

"This is a strategy for the bacteria to survive after a ton of water is
added and there's no oxygen for them in the soil," Krichels said. "When
that happens, instead of oxygen they use nitrate, and breathe out
nitrous oxide, a process called denitrification." Unlike fertilization
in agricultural fields, denitrification in deserts may have a different
source of nitrate. "Nitrate pollution in deserts originates from fossil
fuel combustion, not fertilization," Krichels said. "Combustion releases pollution that hangs around, gets deposited into soils over time, and re-emerges after a rain as N2O."


========================================================================== Automobiles or industrial processes send a few different forms of
nitrogen into the atmosphere. "Combined, they're called NOx, and they
can produce tropospheric ozone, which is bad for your lungs and is also
a greenhouse gas.

It is not to be confused with good ozone higher up in the stratosphere
that protects us from UV rays," explained Peter Homyak, UCR environmental scientist and paper co-author.

To determine if fossil fuel byproducts could drive the desert
denitrification, the researchers picked two Southern California sites
in the University of California Natural Reserve System. They used a box "resembling a coffin," Krichels said, with instruments to measure the
chemical composition of air emerging from the soil after the addition
of nitrate.

The box also contained an air conditioning unit, as temperatures often
reached 120 degrees. "Temperatures much higher than 100 degrees Fahrenheit
are thought to prevent microbial processes. Given the heat at our sites,
it was surprising to see so much N2O," Krichels said.

Krichels, who previously studied similar processes in Illinois cornfields,
said what emerges from deserts after rains is 10 times higher than
anything he saw in the Midwest. "The rates of emission are really high,
but short lived," he said. "This only occurs when water is added to
dry soils." Much evidence suggests droughts are becoming more common
globally, and that these droughts will be punctuated by large rain
events. Since droughts dry out soil, these climate changes will make
drying and wetting cycles more common and increase the likelihood that
these processes will become more important sources of greenhouse gas.

Moving forward the researchers will replicate the study with sites
in Riverside and Joshua Tree, to measure whether proximity to cities
increases post-rain nitrous oxide emissions from soils.

In general, Krichels said he hopes awareness of these results moves people
to limit fossil fuel emissions that drive desert soil denitrification.

"On a broader scale, a lot of people don't know these processes happen
in soils in general, or that the nitrogen humans add to the atmosphere
can end up affecting climate change and human health in this way,"
Krichels said. "There's a lot of life in these soils, and it can affect
the entire globe."

========================================================================== Story Source: Materials provided by
University_of_California_-_Riverside. Original written by Jules
Bernstein. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Alexander H. Krichels, Peter M. Homyak, Emma L. Aronson, James O.

Sickman, Jon Botthoff, Hannah Shulman, Stephanie Piper,
Holly M. Andrews, G. Darrel Jenerette. Rapid nitrate reduction
produces pulsed NO and N2O emissions following wetting of dryland
soils. Biogeochemistry, 2022; DOI: 10.1007/s10533-022-00896-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220309104446.htm

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