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	'''Bazzaz, F. A. 1990.''' The Response of Natural Ecosystems to the Rising Global CO<sub>2</sub> Levels. Annual Review of Ecology and Systematics, '''21''':167-196		'''Bazzaz, F. A. 1990.''' The Response of Natural Ecosystems to the Rising Global CO<sub>2</sub> Levels. Annual Review of Ecology and Systematics, '''21''':167-196. Artículo de completo en pdf: [https://www.dropbox.com/s/qkng6jjukel2ntc/Bazzaz1990_Response%20of%20natural%20ecosystems%20to%20the%20rising%20global%20CO2.pdf?dl=0 F. A. Bazzaz, 1990]

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	==Introduction==		==Introduction==
	Evidence from many sources shows that the concentration of atmospheric		Evidence from many sources shows that the concentration of atmospheric

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'''Bazzaz, F. A. 1990.''' The Response of Natural Ecosystems to the Rising Global CO2 Levels. Annual Review of Ecology and Systematics, '''21''':167-196

Artículo completo en:
==Introduction==
Evidence from many sources shows that the concentration of atmospheric
CO2 is steadily rising (61, 17). This rise is strongly correlated with the
increase in global consumption of fossil fuels (104). There are also significant
contributions from the clearing of forests, especially in the tropics (136, 55).
Controversy continues, however, as to whether the biosphere is presently a
source or a sink for carbon (see 52, 54, 56).

Despite this controversy, most scientists agree that rising CO2 levels will
have substantial direct and indirect effects on the biosphere (80). Because
CO2 is a greenhouse gas, its increase in the atmosphere may influence the
earth's energy budget. Several climatologists have used general circulation
models to predict changes in mean annual global temperature (58, 108).

While these models differ in detail, they all predict increased global warming
and substantial shifts in precipitation patterns. Recently, some scientists (60)
have questioned the predictions of these models. But regardless of changes in
global temperature and other climate variables, rising CO2 can influence
world ecosystems by direct effects on plant growth and development.

The large body of literature on the response of crops and intensively
managed forests to elevated CO2 is not treated in this review because there are several excellent and recent reviews of it (e.g. 2, 28, 62, 127, 132 for crops,
and 37, 65, 111 for trees). Instead, this review concentrates on the response of
natural vegetation to elevated CO2 and some of the predicted climate change.

The review addresses the CO2 response of individuals at the physiological
level and the consequences of that response to population, community, and
ecosystem levels. It must, however, be emphasized that most of the findings
on the physiological and allocational response to CO2 were first discovered in
agricultural crops, and that much of the initial work on plants from natural
ecosystems (69) tests the variation among species in these responses.

==Conclusions==

It is clear from this review that some general patterns of response of plants,
especially at the physiological level, to the rising CO2 and the associated
climate change are beginning to emerge (Figure 1). Enhanced photosynthesis
and growth, increased allocation to underground parts, and particularly water
use efficiency have been strongly documented. However, photosynthesis and
growth enhancement in some species can be of limited duration, perhaps
because of shortages of sinks and the resulting simulation of photosynthates in
leaves. It is also clear that CO2 interacts strongly with other environmental
factors, especially nutrients and temperature, to generate the response at the
individual level.

Work at the community and ecosystem level has clearly shown that, in
most situations, the response at the individual level may become highly
modified and may not predict the response of communities. It is quite likely
that the impact on productivity of ecosystems may result mainly from changes
in species composition brought about by differential species response to
elevated CO2. The number and the identity of neighboring plants, the levels
of environmental resources, the activities of herbivores, pathogens, and
symbionts are crucial to the way plants respond to elevated CO2. Because
of the complexity of these interactions, and our limited knowledge of them,
our predictions about the future impact of the rising CO2 and associated
climate change are very tenuous. In fact, for some ecosystems we cannot
presently even predict the direction of the change that would result from
increasing CO2. Nevertheless, the work on a model system of annual plants,
and with other assemblages, is giving us some insights into the mechanisms of
the response to CO2 at the community level. We are beginning to identify
certain parameters that seem to explain significant amounts of the response
to elevated CO2. For example, initial relative plant growth rates and biomass
allocation seem very important determinants of plant response to
CO2. Responses at the population level are essentially unknown, but that
research in this area, particularly plant-animal interactions, will be of great
importance in understanding the future of biological systems in a high
CO2 world.

[[categoría:bibliografía]]

Bazzaz, F. A. 1990. - Historial de revisiones

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