In future, climate change will bring an increase in salty surfaces on the Earth and in the concentration of CO2 in the atmosphere. However, this higher CO2
has some positive effects on the physiology of barley plants and
increases its tolerance to salinity. This is the conclusion of the PhD
thesis of Ms Usue Pérez-López, defended at the University of the Basque
Barley is one of the most important crops
in the world. In fact 56 million hectares are under barley crops,
making it the fourth most grown cereal worldwide. It is widespread over
all the Continents, given that it adapts very well in different
habitats. As with other plants, the correct development of barley
depends on a suitable balance between the availability of water,
nutrients and CO2. Nevertheless, it is predicted that there
will be an increase in salinity in the soil in future, causing various
imbalances which will result in a reduction in the growth of barley.
According to a number of authors, an increase in the CO2
level in the atmosphere may mitigate this growth decrease of the plants
caused by high concentration of salts. However, research to date
differs as regards results, and it is not known if the increased levels
of CO2 can mitigate the negative effects of salinity on
barley. This question was addressed by UPV/EHU teacher, Usue
Pérez-López, in her PhD, presented at the University’s Faculty of
Science and Technology: Physiological responses of barley to the interaction of salinity and increased CO2. Prospects with climate change.
Ms Pérez-López, a graduate in Biological Sciences with an Extraordinary
Degree Award, carried out her work under the direction of doctors
Alberto Muñoz-Rueda and Amaia Mena-Petite, from the Department of Plant
Biology and Ecology. Dr. Pérez-López developed part of her research at
the Department of Chemistry and Agricultural Biotechnology of the
University of Pisa (Italy).
Greater rates of salinity and CO2
to data supplied by the Food and Agriculture Organization of the United
Nations (FAO), some 20% of irrigated arable surface area is subject to
some level or other of salinisation, thus being hostile terrain for
agriculture. Moreover, it is predicted that, in the near future,
salinity will increase due to factors such as the expansion of
irrigated zones, inefficient irrigation systems, the use of poor
quality water and the increase in soil water loss due to greater
evaporation as a consequence of high temperatures.
result of this increase in salinity the hydric state of barley plants
will deteriorate and imbalances in their nutrition will occur due to
excess sodium and chlorine (components of salt) and due to lack of
potassium, calcium and nitrogen. In essence, the plant will produce
less carbohydrates and proteins, which means a reduction in its growth.
The Intergovernmental Panel on Climate Change (IPCC) predicts that the CO2
concentration in the atmosphere at the end of the XXI century will
double current levels. An increase contributed to by human activity
through the combustion of fossil fuels and the destruction of forests.
However, Dr. Pérez-López believes that barley could benefit from this
increase, at least as regards mitigating the negative consequences of
high salinity. Her research was based on the hypothesis that the
greater the concentration of CO2, the higher the rate of
photosynthesis, the hydric state of the plant is enhanced due to its
lower transpiration (losing less water) and absorbs less toxic ions and
is better protected against oxidation.
Dr. Pérez-López selected two varieties of barley (Hordeum vulgare cv Alpha and Hordeum vulgare cv Iranis)
and studied their development, their nutritional and hydric states,
their antioxidant system and carbon and nitrogen metabolisms, under
high salinity and CO2 conditions, both separately and together.
Positive effects of CO2
One of the goals of Dr. Pérez-López’s thesis was to see if the increased CO2
levels would enable less chlorine and sodium to be accumulated in the
tissues of the barley plant. After undertaking a study of the various
plant organs, she concluded that CO2 does not mitigate the accumulation of sodium in the tissues, despite the plant showing greater growth and less transpiration.
This lower transpiration, cause by the presence of high concentrations of CO2,
does attenuate the loss of water through the plant leaves, due to the
fact that the stomas are kept closed and the plant tissues are
dehydrated to a lesser degree. Moreover, Dr. Pérez-López observed that
plants growing under these conditions show greater root development,
which augments the surface for water absorption. As a consequence,
deducing from Ms Pérez-López’s thesis, high levels of CO2 considerably enhances the hydric state of barley.
Dr. Pérez-López also asked herself if higher concentrations of CO2 in the atmosphere mitigate the reduction in growth caused by salinity. According to her PhD thesis, high concentrations of CO2
have a positive influence on the photosynthesis of the plant because,
despite the fact that the plant keeps its stomas shut, the diffusion of
CO2 between the exterior and the interior of the leaf is greater.
Dr. Pérez-López determined the oxidative stress level of the barley
(the oxidation suffered by a plant due to high salinity), studied its
antioxidant capacity, that is its defence mechanisms. Her conclusion
was that high concentrations of CO2 alleviate this stress.
In short, Dr. Pérez-López’s research concludes that the increase in CO2
enables greater growth of barley plants subject to saline conditions,
thanks to the improvement in their hydric state and turgescence, but,
above all, to the increase in photosynthesis.
Elhuyar Fundazioa. Public release date: July 7, 2008.