When a blistering heatwave struck a group of grapevines in Portugal, the end seemed nigh for these fruit-bearing plants. Temperatures rose to a scorching 42C (107F) during the day. But not all of the grapevines facing this onslaught were alike: some had a secret weapon.
The heatwave was actually an artificial one, created in a laboratory to mimic the kind of conditions that large parts of southern Europe are, coincidentally, experiencing this summer. The scientists who carried out the experiment had treated some of their vines with a special cocktail of bacteria from an unlikely source: Spanish salt marshes. While all the vines were kept watered, they were exposed to punishing heat.
“It was quite surprising,” says João Carreiras, a PhD candidate in marine and environmental science at the University of Lisbon. “I expected some results but maybe not so significant.”
Vines whose roots had been exposed to one group of bacteria fared unexpectedly well. They didn’t wilt or develop discoloured leaves, unlike some of the other plants. They barely showed any signs of heat stress in their cells. For them, it was like the heatwave hadn’t really happened.
Carreiras and his colleagues have yet to discover why the microbes had this effect. However, they hope their research could help wine producers protect their vines from the increasingly harsh and variable weather caused by the climate crisis.
Grapevines – like all plants – have their own microbiome that helps them stay healthy and grow. Introducing marine bacteria could bestow extra hardiness on them (Credit: Alamy)
Heat stress can make the grapes used in winemaking unpleasantly bitter, resulting in unbalanced wines. Severe heatwaves also damage or even kill grapevines. Climate change is already making heatwaves more likely across the globe, sometimes with devastating effects. “It can destroy a whole field,” says Carreiras. (Read more about how climate change is tweaking the taste of wine.)
The idea of treating plants with microbes from harsh environments, to see if that improves their growth or resistance to various stresses, has been around for decades. Researchers in the 1990s explored the concept of using bacteria found in the oceans. More recently, improvements in DNA sequencing technologies have allowed scientists to analyse marine microbes in detail, meaning that they can identify which ones might have plant growth-promoting properties.
Why treat grapevines with bacteria from salt marshes, specifically? The idea is that plants that grow in the salty conditions in these marshes must be able to cope with tough conditions. “They can endure stresses that not many plants come close to – salinity, heat, pollution, heavy metals,” says Carreiras. The microbes associated with these plants, their microbiome, have presumably also evolved to thrive in such an environment. Those microbes might have a protective effect for plants, Carreiras suggests.
The lab experiment Carreiras and his colleagues carried out involved growing the grapevines under controlled conditions for a few months and then dividing them into groups. The team applied a solution containing mixtures of bacteria collected from the salt marshes to some of the groups in the weeks leading up to the heatwave. Then they whacked up the heat.
Afterwards, the team analysed the leaves, for example shining strong lights through them to show up the structure of cells. This revealed that the vines treated with the second bacterial collection were barely affected by the heat. Usually, one would expect to see damage to the plant’s cell walls after such an assault, says Carreiras, but for those grapevines very little such damage was visible.
“Microbes have been adapting and evolving for thousands of years,” says Katherine Duncan, a microbial chemist at the University of Strathclyde who searches for new drugs that are produced by marine bacteria. “It makes sense to look to them for natural solutions.”
However, the application of microbes to crops is still in its infancy, Duncan cautions. She says it will be important to work out how much farmers might have to tailor microbial species to particular plants.
Unsettled weather
“I think it’s interesting that they went to marine sources,” says António Graça of Sogrape, a wine company in Portugal. Graça has a working relationship with one of the authors of the paper, though was not involved in the study. Separately, Sogrape is exploring the application of marine algae extracts to grapevines, to see if that helps the plants cope with drought.
Under pressure from drought and heatwaves, vineyards are using technology like drip irrigation to help them cope, but it isn’t always enough (Credit: Alamy)
The challenge facing vineyards is not any one kind of weather, says Graça, but rather increasing variability. “We are seeing very extreme variations between winter and summer and from year to year.” As a result, if microbes are to help, researchers must show that they can improve plant growth and stress tolerance out in the field, rather than merely in lab studies.
Carreiras and his colleagues are already working on that, with the help of a “very interested” local wine producer.
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In May, the researchers mixed some of their bacterial collections with water and applied the treatment once a week for a month to rows of 16-year-old and newly-planted grapevines in a Portuguese vineyard. The current heatwave will put them to the test.
Carreiras adds that he and his colleagues are already working on alternative methods of applying the bacteria – from putting them into granules that can be added to soil to embedding them with grapevine seeds.
The final step will be to ensure that the wine is drinkable. Graça says researchers will need to show that the microbes don’t induce any unwanted changes in acidity or sugar levels, which would jeopardise the flavour of the grapes and any wine made from them. Carreiras and his colleagues haven’t yet tasted grapes produced from the vines in their experiments, though they plan to in the future.
Given the pace of climate change, winemakers urgently need ways to secure their crops. Nevertheless, Carreiras is hopeful that fine-tuning the microbiome of these valuable plants could help farmers adapt.
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