This miniseries is dedicated to our planet earth, so we may better
appreciate how she lives and sustains all creatures large and small, that we
may learn to dance to the complex rhythms of her life music without stopping
her in her tracks.
Space scientist and inventor Jim Lovelock first proposed in the 1970s
that the entire earth is a self-organizing, self-regulating entity, rather like
an organism. He named the earth Gaia, after the Greek earth goddess.
The idea that Gaia is alive and has a life of her own immediately caught
fire. It inspired many earth scientists to look for the dynamic processes that
organize and regulate the currents of the earth, to make a congenial home for
all her inhabitants. These scientists are richly rewarded.
Records from ice and deep sea cores show detailed globally correlated
changes going back at least 800 000 years, leaving us in no doubt that the
earth behaves from moment to moment as one coherent whole, just like an
Not only can we can read Gaias life-history from her deep memory
stores, we can also tune in to her life-force pulsing as she is living
Gaia spinning in her perpetual dance around the sun, her mighty breath
tumbling from hot belly to the poles, swirling across the continents, bringing
welcome rain to forests, grasslands and crops, or torrential downpours, floods
and hurricanes. Vast slow vortices of water connect her oceans from the
furthest northern reaches to the southernmost haunts, from the shimmering sea
surfaces to the dark deep beds, distributing warmth and nutrients, sustaining
life with life.
Gaias breath is our breath, her water our water. Let Gaia live
that we may live.
More carbon dioxide doesnt just make the earth warmer. It is an
entire conglomerate of correlated changes of global dimensions in the
earths climate, water, land, and not the least of all, her living
inhabitants. Dr. Mae-Wan Ho
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Complex response of plants to CO2
The most significant, quantifiable indicator of climate change is the
accumulation of carbon dioxide and other green house gases resulting from
excessive burning of fossil fuel and industrial chemical emissions. The current
rates of change in the chemical composition of our atmosphere are without
geological precedent. The increase in CO2, in particular, will have
important consequences on photosynthesis, the process whereby green plants
create carbon compounds from carbon dioxide to feed human beings and much of
the living world. CO2 concentrations were as low as 180ppm only 18
000 years ago, at the peak of the last glaciation. Current CO2
concentrations are double that, and are predicted to exceed 550ppm during the
second half of the present century, i.e., double the pre-industrial
The rate of photosynthesis depends on CO2 concentration. For
most plants, the rate of photosynthesis is still not saturated at current
CO2 concentrations in the atmosphere, and so there is room for more
increase in carbon dioxide fixation. In the early days, this response was
considered everything there is to understand about the effects of
CO2 on photosynthesis. But things are actually more complicated,
because apart from photosynthesis, the plant carries out a host of other
metabolic reactions, all interconnected, which have to be balanced. A greater
abundance of some chemical does not necessarily enhance the availability of
other chemicals. Furthermore, CO2 concentration affects the
plants water budget, which will impact on the photosynthesis. Finally,
plants interact with animals, and an increase in CO2 will have
impacts on the animals.
Response to CO2 depends on environmental conditions
There are very few relevant observations on the impacts of increased
CO2 on plants and the associated ecosystems, especially forest
ecosystems, which account for close to 90% of the carbon pool. Over short
periods of time, plants can grow faster under elevated CO2 as long
as the roots and mycorrhiza (beneficial fungi that grow in association with
plant roots) have not fully exhausted the available nutrients in the soil. But
sooner or later, elevated CO2 will have negative impacts on nutrient
Similarly, isolated tree seedlings, or orchard trees receiving an
optimal resource supply including light from almost all directions, and
horticultural plants supplemented with fertilizers, can all show increased
growth in response to a 200-300ppm increase in CO2 concentration.
But these effects disappear under more realistic conditions. Very few or no
such responses are seen in unfertilised grassland and in dense tree assemblages
on unfertilised ground. In some experiments, plants did not even grow more in
elevated CO2 despite being supplemented with mineral fertilizers. A
clear nutrient-dependence of the CO2 growth response was found for
tropical trees grown in ample light on either unfertilised or fertile
The type of soil also matters. In one experiment, two contrasting
forest soil types were used with young beech and spruce grown jointly (as they
do in nature) on acid or calcareous forest soil from the Swiss central plains.
The results "must be a shock" to anybody involved in CO2 research,
says Christian Korner the Institute of Botany, University of Basel,
Switzerland. The responses were in opposite directions depending on the soil
type. In a calcareous soil, beech grows better, whereas in acidic soil, birch
predominates. Neither elevated CO2 nor fertilizers alters the basic
Much of the response to CO2 comes during the early stages of
growth, when resources (nutrients, space and light) are plentiful, but drop off
in the later stages. Often it is not a single nutrient, but the interaction
between nutrients that determines the CO2 response. For example,
legumes with nitrogen-fixing symbionts are often particularly responsive to
CO2 enrichment, but only when supplemented with phosphate. Under
some conditions, CO2 enrichment may even induce symptoms of nutrient
deficiency. It appears that a carbon-rich diet can lead to the export of
soluble carbon compounds from the roots, which in turn may cause the food web
around the plant roots to tie up free nitrates. Several years of in situ
CO2 enrichment of calcareous grassland caused a drastic reduction of
free nitrate in the soil solution; and the more diverse the plant communities,
the more pronounced the effect, possibly due to the more effective exploitation
of the carbon substrates by soil mycorrhiza.
Response to CO2 affects water budget in a species-specific
manner and impacts on the ecosytem
It is widely known that CO2 enrichment tends to reduce the
opening of stomata (pores) on the leave surfaces, thereby restricting
consumption of water. This is so for grassland species and crops, as well as
for young trees grown in open-top chambers.
However, when tested in situ on tall trees, no such response was
found in conifers, and in important broad-leaved species such as European
beech. Other species such as hornbeam, showed a significant 20% reduction,
while other species are intermediate. In other words, much depends on the
Soil moisture tends to be higher under vegetation that close up their
stomata as CO2 increases, thereby favouring species that are not
drought resistant over those that are. In calcareous grassland, this
moisture-saving response induced a significant stimulation of species such as
Carex flacca and Lotus corniculatus. An unexpected side effect of
this was to stimulate the activity of earthworms by 30%. The current evidence
for grassland responses to elevated CO2 suggest that most if not all
the biomass increases are due to such indirect effects on moisture.
All of this makes predictions very difficult, because how forests,
grasslands and crops will respond to increase in CO2 will depend on
the species present and the state of the soil.
Changes in live tissue composition species-specific and impacts on
There are many examples in which elevated CO2 leads to
sustained changes in live tissue composition, with carbohydrates commonly
increasing, proteins decreasing and secondary compounds varying in response.
Carbohydrate/protein ratios were also significantly increased in plants growing
for many generations around natural CO2 springs, also in leaves of
tropical trees experiencing elevated CO2 levels in situ
either in deep shade or in the fully sunlit forest canopy, and at the Swiss
Canopy Crane site, where a mature forest has been continuously exposed to
increase CO2 atmosphere for two years.
The shoots and leaves of the forest trees are found to have more
carbohydrates, and insects feeding on such leaves show significant differences
in growth rates, dependent on the species of trees. Thus, caterpillars of the
moth Lymantria dispar showed a 23% reduction in growth rate on oak
exposed to elevated CO2 compared to those on control oak trees; but
on hornbeam trees, the precise opposite was found, a 28% increase in growth
rate on trees exposed to elevated CO2 compared to controls.
An earlier test found that caterpillars of Lymantria monacha
grew more and consumed proportionately less per unit body mass when fed on high
quality, nitrogen-rich spruce needles produced under decreasing CO2.
Leaf chewers like Lymantria can compensate for diminished food quality
to some extent by increasing the amount of leaf consumed. Other species like
leaf miners, apparently, dont have this option, and will suffer more as a
result. These observations point to a broad spectrum of effects on biodiversity
across the trophic levels.
Impacts on decomposers
Rates of decomposition of leaf litter is another important factor
affecting ecological health. This has mostly been found to remain unchanged.
However, when different litter species were fed to specific species, it became
obvious again that the results depend on the species. The isopod Oniscus
asellus clearly shifted its preference from Fagus to Acer
under CO2 enhancement, with no change on Quercus.
Some major consequences observed
All the responses to elevated CO2 described so far are
species-specific. The effects may be direct or mediated via effects on moisture
and metabolism. Similar species-specific responses of far-ranging ecosystem
consequences are found when nutrient availability increases, or when
temperature rises, two other key facts of global change. Thus, major changes in
biodiversity can result from global climate change.
In forests, climbing vines or lianas can take particular advantage of
CO2 enrichment in deep shade, partly because of the shift of the
light-compensation point of photosynthesis to low light intensities. This
increases the likelihood of lianas reaching the forest canopy. Given that the
dynamics of natural forests, tropical ones in particular, are strongly
influenced by the vigour of lianas, this biodiversity effect can overrun the
direct growth effects of CO2 enrichment on canopy trees.
In the temperate zone, Hedera helix can become a serious forest
threat when severe winters become less frequent, as is happening right now. As
long as the forest canopy was open as was the case in 1995 - there was
little stimulation of Hedera under CO2 enrichment. However,
by 1998, the forest canopy closed up, and the under storey light was reduced to
1% of the above canopy sunlight. The biomass of Hedera increased four to
five fold, and increased by another 30 to 40% under CO2 enrichment,
irrespective of nitrogen supply. At the same time, the initial strong biomass
response of the whole tree assemblage was reduced to nearly zero.
Similarly, tropical lianas took enormous advantage of CO2
enrichment in very dim light, overgrowing and driving tropical forests into
faster rotation and reduced carbon storage. When grown on native soil in a
simulated typical Yucatan under storey climate, three native lianas exhibited
strong responses under the current range of atmospheric CO2
enrichment (280 to 420ppm). At higher concentrations, responses became
diminished and even reversed, highlighting the nonlinear responses to
The best data currently available are for grasslands, which are highly
disturbed systems, commonly requiring cutting, grazing or burning to be
maintained. Pulsed canopy expansion refers to reoccupation of
empty space; and is a situation where CO2 enrichment can
be most effective. The two natural grasslands in this comparison, the alpine
and the semi-desert grassland, show very little or no growth response to
CO2 enrichment. Remarkably, the small, insignificant semi-desert
assemblages response is driven by a single species out of about 25
species, in fact, one out of the 5 legumes species in this community. This kind
of response may also hold for complex forest ecosystems as well. It is only
their slow development that has so far prevented us from detecting such
clear-cut biodiversity effects.
To summarise, four main messages emerge from current findings.
Plant species respond differently to CO2 enrichment
(irrespective of the type of response involve), and these biodiversity effects
translate into ecosystem responses.
The responses depend on soil type, nutrition, light, water and
The quality of plant tissue and exudates from roots change (more
carbon, less of other elements), so consumers of plant products are
Responses to CO2 concentration are nonlinear, with the
strongest relative effects under way right now, and few additional effects
beyond about 500 ppm.
Given the globally uniform enrichment of the atmosphere with
CO2, all regions should be affected in some way or other. There is
no ground for complacency. Increase in CO2 does not translate into
an increased in carbon fixation in photosynthesis; no increase is likely in the
longer term. On the contrary, biodiversity may decrease, while the carbon cycle
may speed up, making forests and other ecosystems less effective in
sequestering carbon dioxide, thereby exacerbating global climate change.