SPIRIT
OF PLANTS: STRATEGY
On December the 1rst, the
prestigious Princeton University, published on its web page an article entitled
"Theory of 'smart' plants may explain the evolution of global
ecosystems", published shortly before in the very serious journal Nature
Plants.
Smart plant?
The author of the theory, Lars
Hedin, professor and director of the department of ecology and evolutionary
biology at Princeton, said "Our
theory explains biomes based on the new idea that we must consider plants to be
smart and strategic". And also "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."
For those who don't know, a biome
or biotic area is "a formation of plants and animals that have common
characteristics due to similar climates and can be found over a range of continents"
(Wikipedia definition).
The theory is based on the
observation of plants, of legume family for most, which have the ability to
extract from the air, the nitrogen, essential to their development, while other
plants must extract it from the soil.
Rhizobium on roots (extract from The Oxford Journal)
“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”.
Lars Hedin explains: “Generally we think of plants as responding
passively to their environment, but we found that they can in fact be quite
strategic. Our theory suggests that the distribution of nitrogen fixers across
biomes, and the great success of fixers in tropical forests, is a result of the
evolution of 'smart' plant strategies in tropical forests in particular”.
The study worked on two different
climatic situations.
On one side, tropical forests, and
on the other side temperate and boreal forests. Their role in these situations
is directly related to the recovery of disturbed soils (floods, landslides,
fires, etc.).
In
tropical forests, soils are naturally high in
nitrogen, and paradoxically, legumes are extraordinarily powerful, numerous and
diverse. They use their self-generation of nitrogen capacity for feeding
abundantly in their juvenile phase, allowing them to dominate. At the same
time, the excessive nitrogen is widely used by neighboring plants which benefit
to also have a powerful growth. This explains the extraordinary ability of
tropical forests to recover, in record time, the devastated or abandoned by
humans areas.
Then, nitrogen production becoming
excessive, they "turn it off" in order to save the energy their
exchange with rhizobia requires, to redirect it to their growth needs, in their
battle for solar energy, in an environment where the vegetation thickness is a
limiting factor. This allows them to live very long years. This is a strategy
for powerful growth, wherein the nitrogen-fixers first promote the biome
overall growth by generating a large amount of nitrogen. Then they reduce or
stop this "altruistic" and exhausting action, to stay in a situation
of domination.
In
temperate and boreal forests, where the soils are much
poorer in nitrogen and slower to regenerate, scientists expected to see a clear
dominance of legumes. Yet it is not. In fact they use their capacity otherwise.
They are present, of course, but so much more anecdotal. Their role becomes
crucial in a situation where it's necessary to regenerate the soil after a
fire, for example. They will use a different strategy, in which they will
produce a large amount of nitrogen during the juvenile phase, to allow their
non nitrogen generator entourage to recover health. But in these poorer soils,
legumes don't "turn off" the nitrogen generation, so that they
exhaust themselves to the task and are dominated by other species in the
struggle for sunlight. This strategy to help the survival of other species and
biome usually ends up being counterproductive, since with the depletion of
legumes and their gradual disappearance, soils start again getting poorer.
"Tropical nitrogen-fixing plants are “smart” enough to know when to use
costly nitrogen fixation to compete with neighboring plants, and when to turn
it off, as if they are sentient beings," Lars Hedin explains. "Nitrogen fixers in non-tropical zones are
initially super competitors but end up fueling their own demise. Because their
fixation is not strategic in the long term, they spread nitrogen around to
their neighbors and their neighbors overcome them."
Benjamin
Houlton, terrestrial biogeochemistry professor at the University of Davis (who
was not involved in this research) estimates that this work will allow progress
in "our search for an evolutionarily coherent theory for ecology." He
adds that these plants could be able to adapt to global warming.
Design by César Mejías from the article of El Definido
As
stated in the conclusion section of the Chilean web magazine El Definido (in
spanish) on the same subject
“What does that mean for us humans? What if
one day we are beginning to suffer the consequences of climate change, it is
better that we are surrounded by tropical nitrogen-fixing plants”.
This
leads us to think that plants are organized into societies, biomes, in which
each plant or group of plants plays a special role, useful to the entire biome
and in which power struggles exist, variable according to surrounding
conditions.
Well, it would remind me a little
animal and human societies, right?
Aucun commentaire:
Enregistrer un commentaire