Date palms win over Finland

A newly released study, carried out in the perhaps unlikely location of Finland, has uncovered fascinating new details about the way in which date palms deal with water stress.

It may be a curious place to evaluate one of the desert's great survivors, but in a study in Northern Europe, scientists have been surprised by how resilient the Arab world's fruit-bearing favourite truly is.

No one who has stepped out in the blazing heat of a UAE summer will be under any illusions about how harsh the climate can be.

Thankfully, however, there is the option of wearing a sun hat, moving into the shade or taking refuge in an air-conditioned building.

Plants do not have the option to get up and escape the sunlight. They are rooted to the spot and have to deal with the worst weather thrown at them.

Along with severe heat, another problem is limited water so the likes of date palms have made countless adaptations to help them cope.

A newly released study, carried out in the unlikely location of Finland, has uncovered fascinating details about the way in which date palms deal with water stress.

Although the study involved cultivars collected from Sudan, these plants belong to the same species, Phoenix dactylifera, as those grown in the Gulf.

The work was published in the Emirates Journal of Food and Agriculture, under the title Growth and Photosynthetic CO2 Responses of Date Palm Plants to Water Availability.

Grown in heated greenhouses with controlled amounts of light, the plants were kept in four different water regimes, including 100 per cent field capacity (the amount of water left after excess has drained away after rain or irrigation) plus 50 per cent, 25 per cent and 10 per cent of field capacity.

The plants were also exposed to varying levels of carbon dioxide.

One finding was that as with many other plants, in date palms the senescence – or ageing – of old leaves was accelerated with water stress.

The process by which plants make food, photosynthesis, requires water and carbon dioxide to produce glucose and oxygen.

So by shutting down these old leaves more quickly the plants cut their water use. These old leaves are not shed, however, as farmers who grow date palms will know.

Perhaps more notable was the way in which the plants were able to continue photosynthesising when water levels were just 10 per cent of field capacity. That is a water level at which some plants would have given up producing food.

Instead, even at 10 per cent of field capacity the rate of photosynthesis in the date palm continued to rise as the concentration of carbon dioxide to which the plants were exposed was increased, all the way up to 1,500 parts per million (ppm).

This demonstrates that even when water stress is very severe, the date palm can keep open its stomata – the pores in leaves through which gases are exchanged – and continue to produce food, indicating a very impressive level of tolerance to drought.

Dr Sakina Elshibli, senior author of the study and a member of the University of Helsinki’s department of agricultural sciences, said the result was surprising, although the reason the plants are able to endure these conditions and keep their stomata open is “difficult to answer”.

“Some plants cannot cope.For the date palm, until the level we tested [1,500 ppm], it’s still increasing. Although water reduced the amount of photosynthesis, the increased carbon dioxide increased photosynthesis,” she said.

The study is likely to prove especially topical.

Although climate change could open up new areas where date palms can be cultivated successfully, there will also probably be a downside.

“The main issue here is that the date palm culture in the existing range will be challenged by more drought conditions,” said Dr Elshibli.

“It is very important to study and update knowledge about date palm plants’ responses and performances under harsher environments.”

Another area of interest to the researchers is a different type of palm, one that is remarkably even more drought-tolerant.

The Medemia palm, found in oases in Sudan and Egypt, has proved valuable because its fibres are useful in, for example, making baskets.

“It grows in places the date palm cannot. It’s very dry and exposed to wind and sandstorms – practically nothing else grows there … it’s something in the plant metabolism. It’s genetic,” said Dr Helena Korpelainen, a principal researcher in the University of Helsinki’s department of agricultural sciences and one of Dr Elshibli’s co-authors.

Few scientists have worked on Medemia, so uncovering details of how the plant’s biochemistry enables it to cope with extreme conditions will prove fascinating and also timely, as this palm tree, which has the Latin name Medemia argun, is critically endangered.

But the researchers in Finland are also keen to find out more about the date palm.

They would like to look in more detail at the differences between date palm cultivars, something that would be useful because “some cultivars withstand drought better than others”.

Date palms are sometimes grouped according to how well they can cope with water stress, with the “dry types” more robust than the “soft types”.

“If you consider each cultivar, the difference is not significant, but when you group them into soft and dry types you find big differences between them,” said Dr Elshibli.

Developing a better understanding of this is, she said, “the next step of the research”.

“We have already been studying genetic variation. There’s quite a bit and some of the variation relates to this [ability to cope with water stress],” Dr Korpelainen said.

So although climate change is likely to bring challenges, farmers are likely to be better able to cope thanks to improved knowledge of how date palms deal with extreme conditions.

Daniel Bardsley is a UK-based freelance journalist and former reporter at The National. He has science degrees from the University of Oxford and the University of East Anglia