Climate Change: Forests in Danger

01 October 2018 - By: Jonathan Smith

Climate Change: Forests in Danger

City Forest- Francesco Ferrini
City Forest. Photo: Francesco Ferrini 


By Jonathan Smith

In light of a changing climate worldwide, important ecosystems such as forests are expected to change rapidly. So what exactly will happen to forests during this major challenge? Investigators in this field met up at a session entitled ‘Climate Change Impact on Urban and Natural Forests’ at the SEB Annual Meeting in Florence to present their answers to this question.

Forests are iconic parts of the landscape, and are hugely beneficial for our health, ecosystem and economy. For example, they trap carbon dioxide from the atmosphere, protect the soil from erosion, and provide shelter and food for animal wildlife. Urban forests may even reduce depression and anxiety in city-dwellers. It is not surprising that the sensitive ecology of forests is threatened by the predicted warmer temperatures, higher atmospheric CO2, as well as droughts, floods and other extreme weather patterns accompanying climate change. Therefore, understanding the threat to forest habitats is crucial to knowing how resilient they are, and better informs our strategies for preparing for the changes. This was the main aim of speakers presenting at the SEB Annual Meeting’s “Climate Change and Impact on Urban and Natural Forests” session. In this article, we highlight the progress of some of the speakers as they tackle this complex task.

A VOLATILE TIME FOR EUCALYPTS

Though it may not be obvious to observers, plants are incredibly dynamic organisms. Unable to move and behave as animals can, these complex chemical factories instead interact with their environment using volatile chemicals released into the air. Not only this, but the specific recipe of volatile chemicals can change according to external factors.

Elizabeth Neilson, from the University of Copenhagen, Denmark, studies these volatiles and how they respond to environmental challenges. “Have you ever smelled cut grass?” she asked. “That smell is the result of volatiles released following damage, analogous to a human calling out a danger warning.” However, direct damage is not the only reason plants have to complain. Fluctuations in weather accompanying global climate change likely affect the volatile emissions of plants. “These could cause changes to plant chemistry, which in turn may affect the behaviour of animals dependent on these plants in the ecosystem, such as herbivores or pollinators,” Elizabeth explained.

To better understand the effect of climate change on the plant chemistry and animal interactions, Elizabeth studies an interesting model organism interaction: the eucalypt tree and the koala. “Eucalypt forests are integral to the ecology of Australia and are a crucial tree for the koala,” she continued. The iconic koala exclusively depends on toxic and nutrient-poor eucalypts for nutrition, sleeping 80% of the day just to survive on this eucalypt diet. “Not just this, but koalas may use volatile chemicals from eucalypts, such as oximes, for scent marking, for example,” Elizabeth revealed. “Overall, even a small imbalance in eucalypt chemistry in climate change could seriously affect koala survival.”

Elizabeth’s research involved an ambitious trip to Australia to directly sample the volatile emission profiles of the eucalypts in the forest. There, her PhD student Mette Sørensen placed bags around different branches of flowering trees and pumped filtered air into and out of the bag to extract the volatiles. The team then measured the volatile emissions from both leaves and flowers using chromatography. “This work is important because it is the first study to target adult eucalypts in forest habitats instead of younger, more accessible plants in plantations,” Elizabeth confirmed. “Additionally, it is the first time eucalypt flowers have ever been sampled in the field.”

This experiment found a complex suite of volatiles released from eucalypt leaves and flowers, whose role remains to be elucidated. “The flowers showed high variation in their profiles that was very species-specific. This may be because it is advantageous for each eucalypt species to attract their own particular pollinators,” Elizabeth noted.

Other experiments growing seedlings under elevated CO2 and temperature conditions also changed the volatiles emitted from these plants. “This shows that climate change will likely affect this intricate communications system,” Elizabeth concluded. “Next, I hope to investigate the effects these changes have on the wider ecosystem, including the effect on koala biology.”

STRESSED OUT CITY TREES

As we wandered around the host city of Florence during this Annual Meeting, we often took refuge from the summer heat under trees. However, urban plants are more than just passive sun-shades; they are themselves sensitive to environmental stresses and require their own protection, asserted Francesco Ferrini, from the local University of Florence. In fact, he suggested that acclimatising these trees in urban environments might help them survive the onset of climate change in Mediterranean countries.

Urban plants have a whole set of unique challenges compared with rural plants. “In the near future, European countries can expect more extreme and unpredictable rainfall, some with more droughts and others with more floods,” suggested Francesco. However, cities have their own microclimates to think about too, as Francesco continued: “Cities are generally around three degrees hotter than rural areas, and have more pollution, poorer soil and competition from construction works.” These factors will likely exacerbate the expected stresses of climate change in the future.

Francesco presented his studies exploring how we can acclimatise urban plants to future droughts in the city. “Our philosophy in this group is ‘simple research, deep investigation’,” he said. His studies involved cultivating plants in nurseries, and then changing a single factor, such as the amount of water available. His team then investigated the changes to the plants on morphological, physiological, biochemical and genetic scales.

Using this method, Francesco’s team found a way help urban plants resist drought shocks. He explained: “If you reduce the water treatment while the young plants are in the nursery, this will toughen them up ready for when they are delivered to the city sites.” This may also help the plants to weather the predicted droughts accompanying climate change.

One obstacle to implementing these measures to protect the plants is the attitudes of the authorities who care for the urban green spaces. “The authorities often do not like the expense of keeping these green areas,” continued Francesco. “We need to make people aware of the huge benefit of these plants for our ecology, as well as our health; this is not a cost, it is a long-term investment.”

Using more innovative culture techniques, it is thus possible to mitigate changes wrought by climate change. “This is not just a local thing,” Francesco explained. “These findings are important because they can help plants in every city around Europe prepare for the uncertain future.”

HEDGING OUR BETS

Hedge plants in troughs, ready for the start of rainfall runoff experiments - credit Tijana Blanusa_opt
Hedge plants in troughs, ready for the start of rainfall runoff experiments Photo: Tijana Blanusa


With increased droughts in the Mediterranean countries will probably come increased flooding in Northern European countries like the UK. Flooding in urban environments takes place when drainage systems are unable to cope with the amount of water entering them, causing huge economic damage to prone areas. Thus, strategies reducing the amount of water entering the drainage systems would help to keep down the costs of climate change.

Tijana Blanusa, from the Royal Horticultural Society, UK, advocated using urban plants to assist with flood prevention. Normally, urban spaces pave over water absorbent soil with concrete and stone, removing any way to reduce water runoff. In contrast, plants and their host soil can do a lot to reduce this runoff. “Maintaining urban plants is substantially cheaper compared with artificial systems,” Tijana related. “Plants are able to capture rainfall and passively assist with flood prevention efforts.”

To promote the flood-prevention potential of urban plants, Tijana carried out studies on species of hedges. “Hedges are comparatively under-studied in this context; they are also very relatable for the general public when we communicate this research,” she explained. She aimed to discover which species of hedge are best able to reduce water runoff. “Different species handle water in distinct ways,” she continued. “For example, we hypothesised that species that evaporate and absorb water more quickly, and those that have a larger leaf and canopy size, would best reduce runoff.”

In her controlled experiments, Tijana simulated rainfall onto different species outdoors and applied a set amount of water to each container, measuring the water runoff from each species. “Hawthorn and Cotoneaster franchetii were the best species for reducing runoff,” she confirmed. “Although hawthorn was slightly more effective, it actually loses its leaves in winter whilst C. franchetii is evergreen, showing that really a mix of species is ideal for adaptability.”

This runoff-reduction benefit is only one of many that plants provide in the urban landscape; Tijana’s work has also included pollution-capturing and cooling effects of different hedge species. In spite of this, green spaces are becoming less common in the UK. “Green spaces need more attention from the public and governmental bodies,” concluded Tijana. “Our studies could convince them that we need to protect and nurture the urban green spaces, not ignore them.

SNAPSHOT OF A DROUGHT

Plants have ingenious systems for supplying water to their various parts. A passive system of evapotranspiration, with evaporation of water from the leaves pulling water up the plant’s xylem from the roots, requires very little energy. However, in times of drought, this sensitive system falls apart, with high pressure differences causing air cavities in the xylem and veins, damaging them and killing the plant.

This is therefore a highly important consideration in a world undergoing climate change, with more extreme droughts and rainfall patterns expected. Timothy Brodribb, from the University of Tasmania, Australia sees this taking place in forests around Australia. “Forests are threatened with drought conditions here; thus, we need a way to understand exactly how resilient the plant species are, as well as the time course of mortality,” he elucidated.

In order to understand when cavitation happens in a plant, you first need to be able to reproduce it and measure it in the lab. Classic methods for measuring the plant’s vulnerability to cavitation include centrifugation, where a plant is spun on a rotor, causing rapid cavitations, and Computer Tomography (CT) in a synchrotron, used for making amazing detailed images of the structures. “However,” added Timothy, “centrifugation does not always reflect natural cavitation in many species; whereas CT imaging in a synchrotron is expensive, time-consuming and damages the sample.”

Timothy and his collaborators developed a new innovative technique for imaging the occurrence of cavitations in plant seedlings. “It is deceptively simple; you just snapshot a backlit plant every minute with a high quality camera, and use image comparison software to measure moments of the lightning-fast cavitation,” enthused Timothy.

This versatile technique is important because it allows for longitudinal experiments that capture exactly when a plant starts to die from cavitation. Timothy continued: “We have measured the vulnerabilities of different species and even simultaneously measured different plant organs in drought conditions”. For example, using this method in the olive plant, he discovered that the roots of the plant were the most resistant to cavitation in their samples, whereas the largest plant vessels were particularly vulnerable. In another species, the tomato plant, everything was equally vulnerable to cavitation.

Another advantage of this technique is that it is very applicable to conditions in the field. “With these findings, we have been able to apply it to the natural world with amazing precision,” remarked Timothy. “In one instance, we predicted exactly which species would perish first in a drought-stricken area, and our predictions were spot on.” With this work, Timothy aims to expand his efforts and collect collaborators. Furthermore, he hopes to launch more phenotyping projects to inform our efforts combatting droughts exacerbated by climate change.

LESSONS FROM A GENETICALLY-MODIFIED PLANT

Physiological function of biogenic isoprene
Physiological function of biogenic isoprene. Photo: Violeta Velikova


Plants face strong challenges when enduring the extreme consequences of climate change. They cannot simply pack up and move on, neither can they genetically adapt to the rapid changes. Thus, they need to be able to adapt their phenotypes.

Violeta Velikova, from the Institute of Plant Physiology and Genetics, Bulgarian Academy of Sciences, Bulgaria, wants to better understand how native plant species adapt their physiology to these incoming challenges. “This knowledge will be instrumental for helping us to reduce the danger to these plant species,” she said in her presentation.

A key mechanism for physiological adaption in plants is by using biogenic volatile emissions, the most abundant of which is isoprene. “Isoprene influences plant physiology and survival,” explained Violeta. “It affects plant photosynthetic organelles, called the chloroplasts, and is involved in protection from many cellular stressors, such as reactive oxygen species.”

To investigate the role of isoprene in drought protection, Violeta’s team selected Arundo donax, an emitter of isoprene, and Hakonechloa macra, a non-emitter. They then subjected the plants to drought conditions, before rescuing them by rewatering. “Interestingly, the isoprene-emitter, A. donax, recovered its photosynthesis better than the non-emitter,” remarked Violeta. “This indicated that isoprene protects the emitting plant’s vital photosynthetic functions from droughts, while non-emitters invest in other metabolites to cope with stresses.”

Violeta’s team then carried out proteomics on genetically-modified plants to understand the exact effects of isoprene on plant photosynthesis. “Genetically knocking down the isoprene synthase gene in transgenic poplar trees strongly reduced isoprene emission and actually modified protein profile in the chloroplasts,” Violeta described. Isoprene seems to protect photosynthesis by altering the structure of the photosynthetic membranes within chloroplasts, helping them to recover their function after drought stress.

With this knowledge, and strategic study of transgenic models, we now know much more about how some plant species are able to resist the stressors brought on by climate change, as Violeta enthused: “Plant species that emit isoprene are definitely more protected from transient extreme drought events than non-emitters; this informs us much better in our efforts to preserve the habitats undergoing these stresses in the near future.”

TACKLING THE FUTURE CRISIS

The climate is undergoing profound changes in the near future, and this will bring more extreme weather patterns in European countries, such as intense flooding and drought. As has been discussed in this SEB session, many plant species are armed to cope with these changes to a certain extent, however, other species will need help, especially those in the more stressful urban environments.

Saving these plants clearly benefits society. The urban plants talks show that, in fact, these plants provide all sorts of advantages to the urban society such as capturing pollution, cooling down the city environment, reducing rainfall runoff and improving our health and wellbeing. These benefits are not discussed enough in the governmental bodies nor in the public sphere, however, the work of these speakers informs efforts to maintain the benefits of the green spaces. Thus, safeguarding plant life during climate change will be instrumental in preserving the habitats, and animals dependent on them. This is an investment worth making.

Watch out for a collection of articles from this session which will feature in SEB’s journal Conservation Physiology

Category: Plant Biology
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Jonathan Smith

Jonathan Smith served as the SEB’s press intern for the annual meeting in summer 2016, and has since contributed articles for the SEB’s bulletin. After obtaining an undergraduate degree in Neuroscience from the University of Bristol, he is currently studying for a PhD in locust neurobiology in the University of Leicester and runs an active Twitter account communicating his work.

Twitter: https://twitter.com/j_ivories