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TheScientist
EXPLORING LIFE, INSPIRING INNOVATION
By Andy Carstens
October 17, 2022
ABOVE: Mesquite trees and shrubs of the genus
Prosopis don’t need fertile soil to thrive in the desert
because symbiotic
bacteria convert atmospheric nitrogen into ammonia, which the plants
readily absorb. © ISTOCK.COM,
OLBYJOE
Climate Change May Favor
Nitrogen-Fixing Plants
Aridity appears to configure
landscapes with a greater diversity of plant species that rely on
symbiotic bacteria for nitrogen.
To determine how arid conditions affect the
biodiversity of these types of nitrogen-fixing plants, University of
Florida PhD student Josh Doby compared public data on soil, species
counts, and aridity from 47 terrestrial sites in the US. Doby and his
colleagues initially hypothesized that nitrogen-deficient soils would
prompt an increase in nitrogen-fixing plant diversity.
EDITOR’S CHOICE IN ENVIRONMENT
In Death Valley National Park, which
straddles the California-Nevada border, mesquite plants (genus
Prosopis) thrive in extreme aridity. While most vegetation types
must extract most of their nutrients from fertile soil, mesquites and
similar plants receive additional nitrogen from symbiotic bacteria,
which
enzymatically fix atmospheric nitrogen into an easily absorbed
form in exchange for sugars produced during photosynthesis.
To determine how arid conditions affect
the biodiversity of these types of nitrogen-fixing plants, University
of Florida PhD student
Josh Doby compared
public data on soil, species counts, and aridity from 47
terrestrial sites in the US. Doby and his colleagues initially
hypothesized that nitrogen-deficient soils would prompt an increase in
nitrogen-fixing plant diversity. The results, however, showed “that
aridity is actually the primary driver” of phylogenetic diversity,
Doby says. As conditions became drier, the ratio of nitrogen-fixing to
non-fixing plant species increased even as overall plant diversity
declined.
Because these plants have access to
atmospheric nitrogen from their symbiotic bacteria, their leaves
contain more nitrogen than other plants, and this buffers them against
aridity by helping them retain water, says
Mark Adams, an ecologist at the Swinburne University of Technology
in Australia who was not involved in this research. When plants open
their stomata to take in carbon dioxide, water escapes, but nitrogen
stimulates the production of enzymes that improve the efficiency of
carbon uptake, shortening how long plants need to hold their stomata
open, Adams explains. “And that’s the secret [of] nitrogen-fixing
plants.”
These findings add to prior evidence
suggesting that nitrogen-fixing plants will outcompete non-fixers as
the planet continues to warm, says Adams. However, future research
should assess whether fixers generate a nitrogen surplus that could
fertilize the soil, helping other plants withstand harsher conditions
too, he adds. “That’s [the] bigger question.”
J.R. Doby et al., “Aridity drives
phylogenetic diversity and species richness patterns of
nitrogen-fixing plants in North America,”
Glob Ecol Biogeogr, 31:1630–42, 2022.
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