Page 11 - 04 Cotton SA October 2014

Research - Navorsing
Global Warming and Cotton Productivity

There has been much concern worldwide about climate change resulting from global warming and the possible effects
on agriculture and human food supply.

2
ost of the global climate change canopy photosynthesis, CO is also a Cotton in its native state grows as a perennial
scenarios include change in the competitive inhibitor of photorespiration, and shrub in a semi-desert habitat, and as such
Mamount and pattern of precipitation, both of these factors result in increased growth requires warm temperatures. However,
more restricted water availability, and productivity. despite originating from hot climates, cotton
more frequent occurrence of extreme The effects of elevated CO on cotton growth does not necessarily grow and yield best
2
weather events including heat waves, droughts and yield have been studied in controlled at excessively high temperatures. The ideal
and heavy rainfall, longer growing seasons, environment chambers and in field studies temperature range for cotton is reported to be
and possible changing geographical regions (see picture). Both types of studies have shown from 20 to 30°C, and growth and reproductive
suitable for crop production. These changes that when the CO levels were increased from development are inhibited at temperatures in
2
will effect agriculture and necessitate adaptive 350 to 700 ppm, leaf photosynthesis increased excess of this optimal day/night temperature
production practices. This paper reviews the with decreased stomatal conductance, regime. These higher temperatures commonly
effects of global warming on cotton growth with greater total biomass production, and occur in cotton growing regions during
and productivity. flowering and boll development, and
increased boll yield. Photosynthesis and water
use efficiency were increased in these elevated depending on the timing and severity of the
CO conditions. The water use efficiency was stress, can represent a serious limitation to yield.
2
Global Warming Hence, with predicted temperature increases
due to the increased above ground biomass
Over the past 100 years, the Earth’s mean production rather than reduced water use. The from global warming this is likely to become
even more important. However, research has
surface temperature has increased by CO enrichment increased cotton height, leaf shown considerable heat tolerance in wildtype
2
about 0.8°C, with about two-thirds of the area, above-ground biomass, and reproductive cottons and also in varieties grown successfully
increase occurring since 1980, and by the output, but not the total root biomass. in countries with temperatures in excess of
end of the twenty first century, global climate 40°C such as Pakistan. Current research efforts
change is projected to cause increased in the USA are focused on improving heat
temperatures of up to 4.00C (see graph) How cotton will respond to these various tolerance of cotton.
According to the latest Intergovernmental changing climatic parameters.
Panel on Climate Change (IPCC, 2012) report, Cotton yields are likely to increase if CO levels Reproductive growth is generally much more
2
these increases in global temperatures are continue to rise as predicted, and if farmers sensitive to high temperatures than vegetative
attributable to increasing concentrations adapt their agricultural practices to the resulting growth. In cotton, the flowering period is
of greenhouse gases, which trap heat in the climate change. Elevated CO -induced climate reported to be the most sensitive phase to
2
atmosphere, by absorbing and emitting change will affect cotton production practices elevated temperatures and represents a major
radiation within the thermal infrared range, due to a change in the amount and pattern of limitation to productivity which is likely to
and consequently increase temperatures. precipitation, more restricted water availability, become more important with global warming
The primary greenhouse gases in the Earth’s more frequent occurrence of extreme (see picture of flower). This is because successful
atmosphere are carbon dioxide, water weather events including heat waves, droughts pollination, pollen germination, pollen tube
vapor, methane, nitrous oxide, and ozone, and and heavy rainfall, longer growing seasons, growth and subsequent fertilization of the
also aerosols such as chlorofluorocarbons, but possible changing geographical regions ovule (potential seeds) are prerequisites for
CO is the main greenhouse gas. The increased suitable for cotton, increased pests, diseases, seed formation in cotton, and seeds with their
2
2
CO is mainly due to human activities such as and weather extremes.
deforestation and burning fossil fuels, as well >>> 12
as natural processes such as respiration and
volcanic eruptions. Global carbon dioxide
concentration has increased from about 280
ppm at the start of the industrial revolution (ca.
1750) to 398 ppm at present and it is expected
to exceed 550 ppm by 2050.
Effect of Increased CO on Cotton Plant
2
Growth
Carbon dioxide is a major input of
photosynthesis, and increasing ambient CO 2
would enhance photosynthesis and plant
growth. This is because photosynthesis
responses to increasing CO , such that
2
increasing CO levels above the current ambient
2
level would result in higher amounts of CO 2
fixed, and therefore increased carbohydrate
production and enhanced plant growth. It
has been estimated that the photosynthetic
rate of agricultural crops such as cotton would
increase by 33% with a doubling of the CO 2 Fig. 1. Increase in Global Temperatures and Atmospheric CO2 from 1880 to 2010. (WWW.NCDC.
concentration. In addition to enhancing NOAA.gov)

Katoen SA Cotton 11 September 2014