Agriculture Reference
In-Depth Information
including that of host crops, and increase survivability of some organisms,
especially in warmer winters.
17.3.2 CARBON DIOXIDE
The Earth's atmosphere consists of nitrogen (78.1%) and oxygen (20.9%),
with argon (0.93%) and carbon dioxide (0.031%) comprising next most
abundant gases (Lide, 2009). Nitrogen and oxygen are not considered to
play a significant role in global warming because both gases are virtually
transparent to terrestrial radiation. The greenhouse effect is primarily a
combination of the effects of water vapor, CO
2
and minute amounts of
other gases (methane, nitrous oxide, and ozone) that absorb the radiation
leaving the Earth's surface (IPCC, 2007). Because of climate change, the
CO
2
concentrations in the atmosphere have increased approximately 35%
from preindustrial times to 2005 (IPCC, 2007).
There is growing evidence suggesting that many crops (notably C
3
crops) may respond positively to increased atmospheric (CO
2
) in the ab-
sence of other stressful conditions (Long et al., 2004). On the other hand,
the beneficial impact of elevated (CO
2
) can be equalized by other effects of
climate change, such as elevated temperatures, higher tropospheric ozone
concentrations and altered patterns of precipitation (Easterling et al.,
2007). For photosynthesis to occur, CO
2
must diffuse from the atmosphere
towards the chloroplasts. The main gate of entry of CO
2
into the leaf is via
the stomatal pore. Changes in CO
2
concentration in the atmosphere can
alter plant tissues in terms of growth and physiological behavior. Several
studies concluded that increased atmospheric CO
2
alters net photosynthe-
sis, biomass production, sugars and organic acids contents, stomatal con-
ductance, firmness, seed yield, light, water, and nutrient use efficiency and
plant water potential.
Jablonski et al. (2002) evaluated 79 crop and native species at elevated
CO
2
. They found, on average, increases in the numbers of flowers (19%)
and fruits (18%), in biomass per seed (4%), in total seed biomass (25%),
and in total plant biomass (31%). Bindi et al. (2001) studied the effects
of high atmospheric CO
2
during growth on the quality of wines. These
authors observed that elevated atmospheric CO
2
levels had a significant
effect on fruit dry weight, with increases ranging from 40 to 45% in the
550 mmol CO
2
/mol treatment and from 45% to 50% in the 700 mmol CO
2
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