The upsurge in droughts is one of the main consequences of climate change, and affects crops in particular. However, Anabel Robredo, a biologist at the University of the Basque Country (UPV/EHU), has confirmed that in the case of barley at least, climate change itself is providing it with self-defence mechanisms to tackle a lack of water. Climate change is in fact also responsible for a considerable increase in the concentration of CO2, a gas that, paradoxically, is providing this plant with certain characteristics enabling it to offset the effects of drought.
Her thesis is entitled "Physiological Response Mechanisms of Barley to the impact of drought and elevated CO2: adaptation to climate change." Various international publications have also echoed this research, the most recent being Environmental and Experimental Botany.
Basically, Robredo has analysed the effect that takes place in the barley as a result of the combination of two of the main consequences brought to us by climate change: the enriching of CO2 and drought. As the researcher explains, "the atmospheric concentration of this gas has increased considerably within the last few decades, and it is expected to increase much more. So we compared barley plants that grow in a CO2 concentration equal to the current (ambient) one with others cultivated in double the concentration, which is what we are expected to reach by the end of this century." The study was carried out through a progressive imposition of drought so it also determined the capacity of these plants to recover following the lack of irrigation, in an ambient CO2 concentration as well as in the one expected for the future.
More efficient use of water
When discussing plants in general, the effects of an elevated concentration of CO2 were already known. The bibliographical references quoted by Robredo show that this is in fact so, since among other things, this elevated concentration increases biomass, root growth and total leaf area, and alters net photosynthesis rates and efficiency in water use. The so-called stomatal conductance is one of the keys, explains the researcher: "Stomata are pores that plants have in their leaves, and it is through them that they carry out the water and air exchange. When a plant is subjected to a high level of CO2, it closes its stomata to a certain degree. This causes the water to escape less, which is translated into greater efficiency in its use."
So a greater concentration of CO2 would appear to put the plants in an advantageous situation to address droughts. "If they use the water more slowly, they use it more efficiently and can grow over a longer period of time," explains Robredo. At least this is what she has been able to confirm in the case of barley. The results show that even though drought is harmful, its effect on barley is less when combined with an elevated concentration of CO2. In comparison with a situation in which an ambient level of this gas exists, its increase causes leaf and soil water content to fall less, the rates of photosynthesis to be maintained for longer, growth to be greater and the assimilation of nitrogen and carbon to be less affected. The researcher does in fact explain the importance of maintaining the balance between the nitrogen and the carbon: "Both the take-up of carbon and the assimilation of nitrogen have increased in a balanced way."
On the other hand, when irrigation is re-established in barley plants that have been through a drought, its effect has been seen to revert more rapidly to its original state under elevated CO2 conditions, in most of the parameters analysed.
It cannot be extrapolated
So, under future CO2 conditions, the negative repercussions of drought driven by climate change would be delayed further in comparison with the current concentration of this gas. In the case of barley this is so. However, can these results be extrapolated to other crops? As this researcher points out, it is not that simple: "You have to be very careful because plant species often respond very differently, even displaying the opposite. But what we can say is that most plant species tend to use water more efficiently in conditions of elevated CO2 and drought, and that they grow more."
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