When plants suffer heat stress, the effects are far-reaching Reply

By Vasilis Ragousis

Andrea Leigh

Plant ecologist Dr Andrea Leigh’s current research focuses on how plants operate and survive in extreme high temperatures. Image courtesy UTS

The debate about climate change has been going on for years, but the fact is that temperatures are rising. The September of 2013 went on record as the hottest on record, surpassing the previous record of 1983 by more than a full degree. As the temperature keeps climbing, Australia’s plants and crops are facing increasing dangers.

Dr Andrea Leigh, a plant ecologist in the School of the Environment at the University of Technology, Sydney, is interested in arid environments. Her current research is on how leaves operate and survive in extreme high temperatures. In addition, she is the head of a Leaf Temperature Working Group funded by the ARC-NZ Network for Vegetation Function, with the aim of researching the impacts of small-scale microclimatic changes on leaf thermal dynamics.

She spoke at a public lecture on the impact of rising temperatures on human health and the environment at UTS on May 12.

“High temperature extremes are predicted to increase in both intensity and frequency in the future. I am interested in learning how and which plants will survive these increased extremes,” she says.

According to Dr Leigh, the impacts of extreme heat rises are already here. In the Pacific islands, entire populations are being forced to relocate to the mainland as their homes are swallowed by the water while extreme phenomena such as fires and cyclones are becoming more frequent.

“I think the problem is we don’t care so much if species go extinct as long as we can keep eating. Everyone is really sick of seeing a polar bear perched on top of an ice cap.” She says extreme temperatures could mean food and crop shortages but the more immediate threats would disastrous events such as fires and storms. Dr Leigh’s research is focusing on the stress plants suffer from droughts and nutrient deficiency.

“We’ve been focusing on drought stress; nutrients stress is another concern. Most of the soil in Australia is really nutrient poor and so Australian plants have to deal with acute nutrient stress.”

Such impacts can create major problems for farmers and food production. In addition, if plants start dying from the effects of the increased heat, it would harm the local wildlife.

“If you want to look at the grazing industry, for example, and the biodiversity in a grazed landscape – it is much more diverse than biodiversity in a cropped landscape. And I believe it is really important to understand how those landscapes will respond and whether some plants will dominate more… or less. The results so far show us that there are a couple of plants that have thermo-tolerance through the roof, and they are already showing signs of dominating in lots of parts of Australia.”

Dr Leigh says one example is would be the Spinifex, which is able to survive in temperatures as high as 51 degrees. Spinifex is one of those plants that survives bushfires but another factor is its ability to withstand a drought alongside a heatwave, something that would kill most plants.

“We want to know what the species’ composition is going to be like, because in effect if it wasn’t for the plants and the diverse plant community, the animal community wouldn’t exist. Humans wouldn’t exist. You know, there’s sort of this massive flow and effect.”

Dr Leigh believes that in order to understand better what plants will survive, there needs to be more funding on researching the tolerance levels of plants in extreme heats.  “There’s not enough work in thermo-tolerance being done. What has just started picking up globally is thermo-tolerance of plants in the crop area.”

However, Dr Leigh is more interested in the native communities and the diversity of responses; her research has shown that there are many thresholds for different plants instead of only one across the year as was previously believed to be the case.

The grim news is that Dr Leigh thinks it might be too late to avoid the short term effects of the heat.   “We need to be tougher on carbon emissions – it’s just a no brainer. The momentum is such that even if we halt carbon emissions now, there will be a massive lag and they will go on increasing.”

But there is some good news. The thermo-tolerance threshold of plants will be able to rise in order to meet the rising heat.

“Plants, like us, acclimatise through the year. Adaptation is different to acclimatisation. It happens on a slower rate, through years and generations. Acclimatisation is much faster, happening in minutes, hours, days or weeks. The systems are very resilient and in the long term they will bounce back up. Thermo-tolerance thresholds can shift.”


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