Princeton
University researchers suggest in a new theory of land-biome evolution
that plants are
not passive features of their environments, but may instead actively
behave in ways
that determine the productivity and composition of their ecosystems.
The theory was
developed to explain why trees known as "nitrogen fixers," which
produce
their own
fertilizer from atmospheric nitrogen, flourish in nitrogen-rich tropical soils,
but are
short-lived in the nitrogen-poor soils of boreal or temperate forests. The aerial
photo
above shows a
rainforest in Panama in which nitrogen-fixing trees are abundant
(about 10 percent
of all trees), diverse, and persist in both young and old forests.
The researchers
found that tropical nitrogen fixers evolved to stop producing nitrogen
in order to
compete with neighboring trees.
(Photo courtesy of
Smithsonian Tropical Research Institute, Panama)
(December 1, 2015) It's
easy to think of plants as passive features of their environments, doing as the
land prescribes, serving as a backdrop to the bustling animal kingdom.
But what if the ecosystems of the world take their various
forms because plant "decisions" make them that way? A new theory
presented by Princeton University researchers in the journal Nature Plants
suggests that in some cases that may be exactly what happens. In one of the
first global theories of land-biome evolution, the researchers write that
plants may actively behave in ways that not only benefit themselves but also
determine the productivity and composition of their environs.
"Our theory explains biomes based on the new idea that
we must consider plants to be smart and strategic," said senior author
Lars Hedin, a Princeton professor of ecology and evolutionary biology and
department chair. "This is a global theory that explains why biomes differ
in nutrient conditions and in their abilities to respond to disturbances and to
absorb carbon dioxide from the atmosphere."
The researchers developed their theory to solve a
longstanding mystery in ecology of why trees that can produce their own
fertilizer from atmospheric nitrogen grow where they do — they thrive where
scientists suppose they shouldn't, and struggle in seemingly ideal conditions.
These plants, known as "nitrogen fixers," use
secretions to invite soil bacteria known as rhizobia to infect their roots
cells. In exchange for carbohydrates that the plant produces by photosynthesis,
rhizobia convert nitrogen in the air into the fertilizer form plants need, with
excess nitrogen from the host plant eventually creating a nitrogen cycle that
benefits neighboring trees. The majority of nitrogen fixers occur in the
diverse legume family that includes beans and peas as well as trees.