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What a hot SPA can tell us about keeping native plants thriving in extremes

Understanding how best to keep Australian native plants thriving in extremes is becoming more and more important for native seed production in a changing climate.

Luckily, the seed science team at Greening Australia has the perfect testing ground to study how plants respond to extremes: a hot sandy SPA (and by that we mean seed production area). To be exact, the Jarrega SPA, on Yuat Country in Western Australia’s mid wheatbelt region, which has capacity for 100,000 plants across 24 native plant species.

A group of men in the foreground are standing by farm vehicles preparing to plant, with trays of seedlings hanging from shoulder straps. Behind them, stretching to the horizon, rows of young native vegetation can be seen.

SeedX and KMAC put the finishing touches on the Jarrega SPA in WA this year. Photo: Jesse Collins.

So how hot is this SPA?

SeedX and Greening Australia, in partnership with the Kwelena Mamakort Wedge Island Aboriginal Corporation (KMAC), finished planting out the Jarrega SPA this year, but the bulk of the planting was done in May 2023 – six months before WA’s hottest summer on record.

Using a research-grade weather station with in-kind support from Edaphic Scientific, the seed science team at Greening Australia began monitoring the weather conditions at Jarrega in December 2023, and tracked temperatures in real time throughout the hot summer.

They also placed temperature/humidity loggers at 20 cm above soil level, mounted within the crowns of establishing seedlings, and deployed a network of 64 soil moisture dataloggers across the SPA in eight priority species.

A slim weather station mounted on a pole is shown in the foreground, while in the background a wide open field full of guarded native plant seedlings can be seen.

The research-grade weather station instrumentation at Jarrega SPA, supported by Edaphic Scientific. Photo: Edward Tsen / Greening Australia.

“These plants are tough; they evolved to deal with hot and dry extremes. But with the tech we deployed we got a real insight into the conditions from a plant point of view, which is particularly of interest because such hot summers are likely to become more frequent,” said Dr Edward Tsen, a technical specialist in Greening Australia’s seed science team.

“We had a series of heatwaves in February 2024, with 12 days above 40 degrees. Jarrega hit a max of 46°C in terms of air temperature, but at seedling level (20cm above soil) temperatures were up to 54°C. The seedlings experienced more than 200 hours of temperatures above 40°C between January and February, combined with very low humidity.”

A graph shows the extreme heat at Jarrega in February 2024, with temperatures registering even higher at the seedling level (20cm above ground level) than at weather station level (2m above ground).

How can high temperatures and low humidity affect plant growth?

Water in the soil and air is pulled through plants via evaporation from the leaves during photosynthesis. With high temperatures (hot) and low humidity (dry), there’s a stronger pulling force, which places stress on the vessels that plants use to convey water.

A close-up of the crown of a seedling, which has a temperature/humidity logger mounted within the foliage.

Temperature and humidity loggers like this one, set just 20cm off the ground in seedling crowns, give the seed science team a ‘plant eye view’ on conditions.

“One of the main things we’re worried about is that with too much stress, embolisms can occur in these plant vessels,” said Edward.

“That is bad news. It’s like a blockage in an artery. It means the plant loses its ability to transport water, and if it happens enough, the whole stem can die.”

Some Western Australian species have evolved incredible adaptations to deal with this stress and keep plants thriving in extremes; for example, many can tolerate stressful periods by closing their pores, reducing or shutting down photosynthesis, and going into a kind of inactivity to wait out the heat.

A close-up of a Calothamnus quadrifidus flower, which is bright pink.

Some species native to WA, like this Calothamnus quadrifidus, have evolved mechanisms to keep plants thriving in extremes. Photo: Edward Tsen / Greening Australia.

However, the effectiveness of their response depends on the length and severity of the stress, and this can impact their growth and reproduction – which is what a native seed production area is all about.

So what can be done to keep native plants thriving in extremes – not just surviving?

“At Jarrega, the biggest lever we can pull to keep plants thriving and producing at the moment is irrigation. We can ramp up watering on our 220 km of irrigation during stressful periods to help prevent physiological damage in sensitive species, but the trick is also to open the window for growth in plant species that will be able to make use of the extra water,” explained Edward.

Some species at Jarrega still grew substantially despite the heatwaves; for example, some Acacia species added about 2.5 metres of growth over the summer period. This shows that, for them, the growth window was wide open under irrigated conditions.

In a bright sunny field, a row of native plants, all with fine wavy foliage, can be seen disappearing into the distance. The leaves of the nearest plant are clearly blowing in a breeze.

Some species in the SPA grew by several metres despite the heatwaves. Photo: Jesse Collins.

Then again, of the plants lost during the February 2024 heatwaves, the team noted mortality was more prevalent in some species and some provenances (seed source locations) than others. Building a good understanding of this variation in tolerances is ongoing, and vital for managing the current and future growth of plant species with climate change.

The team are also trialling the use of seaweed biostimulants to hormonally improve the stress responses of plants in the SPA.

And what does this have to do with native seed production?

Ultimately, the native seed sector in Australia needs more information to optimise production of genetically diverse, high-quality seed. The team’s experiences at Jarrega show environmental monitoring can be a crucial tool to track plant growth and understand why some species and provenances thrive in extremes, while others struggle.

This information can then be used to help plan for future seed production.

Two people crouch down in a field next to a native plant seedling that has a logger installed beside it. One is examining the leaves of the seedling, while the other is balancing a laptop on their knee and entering data.

Dr Melinda Pickup and Dr Edward Tsen from Greening Australia’s seed science team analyse plant growth and conditions at Jarrega SPA. Photo: Jesse Collins.

“We need to understand how the conditions affect the physiology of our plants to help them not just survive the harsh summers but to get the best growth and performance out of them,” explained Edward.

“By using data from the weather station and soil moisture probes, we can track conditions in the environment and link this to how plant respond. This will help us better understand which species and provenances may be more sensitive to temperature extremes and moisture stress, and enable us to better manage them for growth, flowering and seed set, both now and into the future.”

 
Greening Australia’s seed science team have been tracking plant health and mortality since the first plantings at Jarrega SPA in 2023, as part of a range of experiments for a research project funded by The Ian Potter Foundation. The aim is to build Australia’s knowledge-base on optimal ways to grow native plants for quality seed production.

 
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